diff --git a/packages/loot-core/.babelrc b/packages/loot-core/.babelrc
index 0b04f17c1d..3313ff9ef0 100644
--- a/packages/loot-core/.babelrc
+++ b/packages/loot-core/.babelrc
@@ -1,4 +1,3 @@
 {
-  "presets": ["@babel/preset-env", "@babel/preset-typescript"],
-  "ignore": ["**/__mocks__"]
+  "presets": ["@babel/preset-env", "@babel/preset-typescript"]
 }
diff --git a/packages/loot-core/package.json b/packages/loot-core/package.json
index 9ef7ac840b..baa90b2708 100644
--- a/packages/loot-core/package.json
+++ b/packages/loot-core/package.json
@@ -42,9 +42,11 @@
     "@babel/core": "~7.14.3",
     "@babel/preset-env": "^7.20.2",
     "@babel/preset-typescript": "^7.20.2",
+    "@types/better-sqlite3": "^7.6.4",
     "@types/jest": "^27.5.0",
     "@types/jlongster__sql.js": "npm:@types/sql.js@latest",
     "@types/node-ipc": "^9.2.0",
+    "@types/pegjs": "^0.10.3",
     "@types/webpack": "^5.28.0",
     "adm-zip": "^0.5.9",
     "babel-loader": "^8.0.6",
@@ -67,6 +69,7 @@
     "throttleit": "^1.0.0",
     "ts-jest": "^27.0.0",
     "ts-node": "^10.7.0",
+    "ts-protoc-gen": "^0.15.0",
     "typescript": "^4.6.4",
     "uuid": "3.3.2",
     "webpack": "^4.41.2",
diff --git a/packages/loot-core/src/client/actions/account.js b/packages/loot-core/src/client/actions/account.ts
similarity index 96%
rename from packages/loot-core/src/client/actions/account.js
rename to packages/loot-core/src/client/actions/account.ts
index 55686982b6..6d9ef4350f 100644
--- a/packages/loot-core/src/client/actions/account.js
+++ b/packages/loot-core/src/client/actions/account.ts
@@ -227,12 +227,3 @@ export function markAccountRead(accountId) {
     accountId: accountId,
   };
 }
-
-export function getBanks() {
-  return async dispatch => {
-    dispatch({
-      type: constants.LOAD_BANKS,
-      banks: await send('banks'),
-    });
-  };
-}
diff --git a/packages/loot-core/src/client/actions/app.js b/packages/loot-core/src/client/actions/app.ts
similarity index 100%
rename from packages/loot-core/src/client/actions/app.js
rename to packages/loot-core/src/client/actions/app.ts
diff --git a/packages/loot-core/src/client/actions/backups.js b/packages/loot-core/src/client/actions/backups.ts
similarity index 100%
rename from packages/loot-core/src/client/actions/backups.js
rename to packages/loot-core/src/client/actions/backups.ts
diff --git a/packages/loot-core/src/client/actions/budgets.js b/packages/loot-core/src/client/actions/budgets.ts
similarity index 97%
rename from packages/loot-core/src/client/actions/budgets.js
rename to packages/loot-core/src/client/actions/budgets.ts
index 8684e3cf42..aea8292dfb 100644
--- a/packages/loot-core/src/client/actions/budgets.js
+++ b/packages/loot-core/src/client/actions/budgets.ts
@@ -130,7 +130,7 @@ export function deleteBudget(id, cloudFileId) {
   };
 }
 
-export function createBudget({ testMode, demoMode } = {}) {
+export function createBudget({ testMode = false, demoMode = false } = {}) {
   return async (dispatch, getState) => {
     dispatch(
       setAppState({
@@ -165,6 +165,7 @@ export function importBudget(filepath, type) {
     dispatch(closeModal());
 
     await dispatch(loadPrefs());
+    // @ts-expect-error __history needs refinement
     window.__history.push('/budget');
   };
 }
@@ -193,7 +194,7 @@ export function closeAndDownloadBudget(cloudFileId) {
   };
 }
 
-export function downloadBudget(cloudFileId, { replace } = {}) {
+export function downloadBudget(cloudFileId, { replace = false } = {}) {
   return async dispatch => {
     dispatch(setAppState({ loadingText: 'Downloading...' }));
 
diff --git a/packages/loot-core/src/client/actions/debug.js b/packages/loot-core/src/client/actions/debug.ts
similarity index 100%
rename from packages/loot-core/src/client/actions/debug.js
rename to packages/loot-core/src/client/actions/debug.ts
diff --git a/packages/loot-core/src/client/actions/index.js b/packages/loot-core/src/client/actions/index.ts
similarity index 100%
rename from packages/loot-core/src/client/actions/index.js
rename to packages/loot-core/src/client/actions/index.ts
diff --git a/packages/loot-core/src/client/actions/modals.js b/packages/loot-core/src/client/actions/modals.ts
similarity index 100%
rename from packages/loot-core/src/client/actions/modals.js
rename to packages/loot-core/src/client/actions/modals.ts
diff --git a/packages/loot-core/src/client/actions/notifications.js b/packages/loot-core/src/client/actions/notifications.ts
similarity index 100%
rename from packages/loot-core/src/client/actions/notifications.js
rename to packages/loot-core/src/client/actions/notifications.ts
diff --git a/packages/loot-core/src/client/actions/prefs.js b/packages/loot-core/src/client/actions/prefs.ts
similarity index 100%
rename from packages/loot-core/src/client/actions/prefs.js
rename to packages/loot-core/src/client/actions/prefs.ts
diff --git a/packages/loot-core/src/client/actions/queries.js b/packages/loot-core/src/client/actions/queries.ts
similarity index 100%
rename from packages/loot-core/src/client/actions/queries.js
rename to packages/loot-core/src/client/actions/queries.ts
diff --git a/packages/loot-core/src/client/actions/sync.js b/packages/loot-core/src/client/actions/sync.ts
similarity index 90%
rename from packages/loot-core/src/client/actions/sync.js
rename to packages/loot-core/src/client/actions/sync.ts
index 0c4a7b02fa..81ec013d32 100644
--- a/packages/loot-core/src/client/actions/sync.js
+++ b/packages/loot-core/src/client/actions/sync.ts
@@ -1,21 +1,10 @@
 import { send } from '../../platform/client/fetch';
 import { getUploadError } from '../../shared/errors';
-import * as constants from '../constants';
 
 import { syncAccounts } from './account';
 import { pushModal } from './modals';
 import { loadPrefs } from './prefs';
 
-export function unregister() {
-  return async dispatch => {
-    const profile = await send('unregister');
-    dispatch({
-      type: constants.SET_PROFILE,
-      profile,
-    });
-  };
-}
-
 export function resetSync() {
   return async (dispatch, getState) => {
     let { error } = await send('sync-reset');
diff --git a/packages/loot-core/src/client/actions/transactions.js b/packages/loot-core/src/client/actions/transactions.js
deleted file mode 100644
index e1cd719925..0000000000
--- a/packages/loot-core/src/client/actions/transactions.js
+++ /dev/null
@@ -1,12 +0,0 @@
-import { send } from '../../platform/client/fetch';
-
-import { filterTransactions } from './queries';
-
-export function categorize(accountId) {
-  return async dispatch => {
-    const res = await send('transactions-categorize', { accountId });
-    if (res === 'ok') {
-      dispatch(filterTransactions(null, accountId));
-    }
-  };
-}
diff --git a/packages/loot-core/src/client/actions/user.js b/packages/loot-core/src/client/actions/user.ts
similarity index 100%
rename from packages/loot-core/src/client/actions/user.js
rename to packages/loot-core/src/client/actions/user.ts
diff --git a/packages/loot-core/src/client/data-hooks/accounts.js b/packages/loot-core/src/client/data-hooks/accounts.tsx
similarity index 93%
rename from packages/loot-core/src/client/data-hooks/accounts.js
rename to packages/loot-core/src/client/data-hooks/accounts.tsx
index 405ad6b3ba..d478bc519c 100644
--- a/packages/loot-core/src/client/data-hooks/accounts.js
+++ b/packages/loot-core/src/client/data-hooks/accounts.tsx
@@ -34,7 +34,7 @@ export function CachedAccounts({ children, idKey }) {
   return children(data);
 }
 
-export function useCachedAccounts({ idKey } = {}) {
+export function useCachedAccounts({ idKey }: { idKey? } = {}) {
   let data = useContext(AccountsContext);
   return idKey && data ? getAccountsById(data) : data;
 }
diff --git a/packages/loot-core/src/client/data-hooks/payees.js b/packages/loot-core/src/client/data-hooks/payees.tsx
similarity index 93%
rename from packages/loot-core/src/client/data-hooks/payees.js
rename to packages/loot-core/src/client/data-hooks/payees.tsx
index af440ea06c..cf7b647855 100644
--- a/packages/loot-core/src/client/data-hooks/payees.js
+++ b/packages/loot-core/src/client/data-hooks/payees.tsx
@@ -34,7 +34,7 @@ export function CachedPayees({ children, idKey }) {
   return children(data);
 }
 
-export function useCachedPayees({ idKey } = {}) {
+export function useCachedPayees({ idKey }: { idKey? } = {}) {
   let data = useContext(PayeesContext);
   return idKey && data ? getPayeesById(data) : data;
 }
diff --git a/packages/loot-core/src/client/data-hooks/schedules.js b/packages/loot-core/src/client/data-hooks/schedules.tsx
similarity index 92%
rename from packages/loot-core/src/client/data-hooks/schedules.js
rename to packages/loot-core/src/client/data-hooks/schedules.tsx
index 879f85b53f..4be18b40b0 100644
--- a/packages/loot-core/src/client/data-hooks/schedules.js
+++ b/packages/loot-core/src/client/data-hooks/schedules.tsx
@@ -21,7 +21,8 @@ function loadStatuses(schedules, onData) {
   });
 }
 
-export function useSchedules({ transform } = {}) {
+type UseSchedulesArgs = { transform?: <T>(v: T) => T };
+export function useSchedules({ transform }: UseSchedulesArgs = {}) {
   let [data, setData] = useState(null);
 
   useEffect(() => {
diff --git a/packages/loot-core/src/client/reducers/account.js b/packages/loot-core/src/client/reducers/account.ts
similarity index 100%
rename from packages/loot-core/src/client/reducers/account.js
rename to packages/loot-core/src/client/reducers/account.ts
diff --git a/packages/loot-core/src/client/reducers/app.js b/packages/loot-core/src/client/reducers/app.ts
similarity index 100%
rename from packages/loot-core/src/client/reducers/app.js
rename to packages/loot-core/src/client/reducers/app.ts
diff --git a/packages/loot-core/src/client/reducers/budgets.js b/packages/loot-core/src/client/reducers/budgets.ts
similarity index 100%
rename from packages/loot-core/src/client/reducers/budgets.js
rename to packages/loot-core/src/client/reducers/budgets.ts
diff --git a/packages/loot-core/src/client/reducers/debug.js b/packages/loot-core/src/client/reducers/debug.ts
similarity index 100%
rename from packages/loot-core/src/client/reducers/debug.js
rename to packages/loot-core/src/client/reducers/debug.ts
diff --git a/packages/loot-core/src/client/reducers/index.js b/packages/loot-core/src/client/reducers/index.ts
similarity index 100%
rename from packages/loot-core/src/client/reducers/index.js
rename to packages/loot-core/src/client/reducers/index.ts
diff --git a/packages/loot-core/src/client/reducers/modals.js b/packages/loot-core/src/client/reducers/modals.ts
similarity index 100%
rename from packages/loot-core/src/client/reducers/modals.js
rename to packages/loot-core/src/client/reducers/modals.ts
diff --git a/packages/loot-core/src/client/reducers/notifications.js b/packages/loot-core/src/client/reducers/notifications.ts
similarity index 100%
rename from packages/loot-core/src/client/reducers/notifications.js
rename to packages/loot-core/src/client/reducers/notifications.ts
diff --git a/packages/loot-core/src/client/reducers/prefs.js b/packages/loot-core/src/client/reducers/prefs.ts
similarity index 100%
rename from packages/loot-core/src/client/reducers/prefs.js
rename to packages/loot-core/src/client/reducers/prefs.ts
diff --git a/packages/loot-core/src/client/reducers/profile.js b/packages/loot-core/src/client/reducers/profile.ts
similarity index 100%
rename from packages/loot-core/src/client/reducers/profile.js
rename to packages/loot-core/src/client/reducers/profile.ts
diff --git a/packages/loot-core/src/client/reducers/queries.js b/packages/loot-core/src/client/reducers/queries.ts
similarity index 100%
rename from packages/loot-core/src/client/reducers/queries.js
rename to packages/loot-core/src/client/reducers/queries.ts
diff --git a/packages/loot-core/src/client/reducers/tutorial.js b/packages/loot-core/src/client/reducers/tutorial.ts
similarity index 100%
rename from packages/loot-core/src/client/reducers/tutorial.js
rename to packages/loot-core/src/client/reducers/tutorial.ts
diff --git a/packages/loot-core/src/client/reducers/user.js b/packages/loot-core/src/client/reducers/user.ts
similarity index 100%
rename from packages/loot-core/src/client/reducers/user.js
rename to packages/loot-core/src/client/reducers/user.ts
diff --git a/packages/loot-core/src/platform/client/fetch/index.browser.ts b/packages/loot-core/src/platform/client/fetch/index.browser.ts
index 1c2602cee0..9f4c3a89c2 100644
--- a/packages/loot-core/src/platform/client/fetch/index.browser.ts
+++ b/packages/loot-core/src/platform/client/fetch/index.browser.ts
@@ -2,6 +2,8 @@ import { captureException, captureBreadcrumb } from '../../exceptions';
 import * as uuid from '../../uuid';
 import * as undo from '../undo';
 
+import type * as T from '.';
+
 let replyHandlers = new Map();
 let listeners = new Map();
 let messageQueue = [];
@@ -133,13 +135,17 @@ function connectWorker(worker, onOpen, onError) {
   }
 }
 
-export const init = async function (worker) {
+export const init: T.Init = async function (worker) {
   return new Promise((resolve, reject) =>
     connectWorker(worker, resolve, reject),
   );
 };
 
-export const send = function (name, args, { catchErrors = false } = {}) {
+export const send: T.Send = function (
+  name,
+  args,
+  { catchErrors = false } = {},
+) {
   return new Promise((resolve, reject) => {
     uuid.v4().then(id => {
       replyHandlers.set(id, { resolve, reject });
@@ -156,14 +162,15 @@ export const send = function (name, args, { catchErrors = false } = {}) {
         globalWorker.postMessage(message);
       }
     });
-  });
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  }) as any;
 };
 
-export const sendCatch = function (name, args) {
+export const sendCatch: T.SendCatch = function (name, args) {
   return send(name, args, { catchErrors: true });
 };
 
-export const listen = function (name, cb) {
+export const listen: T.Listen = function (name, cb) {
   if (!listeners.get(name)) {
     listeners.set(name, []);
   }
@@ -178,6 +185,6 @@ export const listen = function (name, cb) {
   };
 };
 
-export const unlisten = function (name) {
+export const unlisten: T.Unlisten = function (name) {
   listeners.set(name, []);
 };
diff --git a/packages/loot-core/src/platform/client/fetch/index.d.ts b/packages/loot-core/src/platform/client/fetch/index.d.ts
new file mode 100644
index 0000000000..646890e9b0
--- /dev/null
+++ b/packages/loot-core/src/platform/client/fetch/index.d.ts
@@ -0,0 +1,23 @@
+import type { Handlers } from '../../../types/handlers';
+
+export function init(socketName: string): Promise<unknown>;
+export type Init = typeof init;
+
+export function send<K extends keyof Handlers>(
+  name: K,
+  args?: Parameters<Handlers[K]>[0],
+  options?: { catchErrors?: boolean },
+): ReturnType<Handlers[K]>;
+export type Send = typeof send;
+
+export function sendCatch<K extends keyof Handlers>(
+  name: K,
+  args?: Parameters<Handlers[K]>[0],
+): ReturnType<Handlers[K]>;
+export type SendCatch = typeof sendCatch;
+
+export function listen(name: string, cb: () => void): () => void;
+export type Listen = typeof listen;
+
+export function unlisten(name: string): void;
+export type Unlisten = typeof unlisten;
diff --git a/packages/loot-core/src/platform/client/fetch/index.web.ts b/packages/loot-core/src/platform/client/fetch/index.web.ts
index 50b02f12e1..db5948454a 100644
--- a/packages/loot-core/src/platform/client/fetch/index.web.ts
+++ b/packages/loot-core/src/platform/client/fetch/index.web.ts
@@ -1,6 +1,8 @@
 import * as uuid from '../../uuid';
 import * as undo from '../undo';
 
+import type * as T from '.';
+
 let replyHandlers = new Map();
 let listeners = new Map();
 let messageQueue = [];
@@ -75,11 +77,15 @@ function connectSocket(name, onOpen) {
   });
 }
 
-export const init = async function (socketName) {
+export const init: T.Init = async function (socketName) {
   return new Promise(resolve => connectSocket(socketName, resolve));
 };
 
-export const send = function (name, args, { catchErrors = false } = {}) {
+export const send: T.Send = function (
+  name,
+  args,
+  { catchErrors = false } = {},
+) {
   return new Promise((resolve, reject) => {
     uuid.v4().then(id => {
       replyHandlers.set(id, { resolve, reject });
@@ -102,14 +108,15 @@ export const send = function (name, args, { catchErrors = false } = {}) {
         });
       }
     });
-  });
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  }) as any;
 };
 
-export const sendCatch = function (name, args) {
+export const sendCatch: T.SendCatch = function (name, args) {
   return send(name, args, { catchErrors: true });
 };
 
-export const listen = function (name, cb) {
+export const listen: T.Listen = function (name, cb) {
   if (!listeners.get(name)) {
     listeners.set(name, []);
   }
@@ -126,6 +133,6 @@ export const listen = function (name, cb) {
   };
 };
 
-export const unlisten = function (name) {
+export const unlisten: T.Unlisten = function (name) {
   listeners.set(name, []);
 };
diff --git a/packages/loot-core/src/platform/server/asyncStorage/index.d.ts b/packages/loot-core/src/platform/server/asyncStorage/index.d.ts
new file mode 100644
index 0000000000..6995ad9f9e
--- /dev/null
+++ b/packages/loot-core/src/platform/server/asyncStorage/index.d.ts
@@ -0,0 +1,20 @@
+export function init(): void;
+export type Init = typeof init;
+
+export function getItem(key: string): Promise<string>;
+export type GetItem = typeof getItem;
+
+export function setItem(key: string, value: unknown): void;
+export type SetItem = typeof setItem;
+
+export function removeItem(key: string): void;
+export type RemoveItem = typeof removeItem;
+
+export function multiGet(keys: string[]): Promise<[string, unknown][]>;
+export type MultiGet = typeof multiGet;
+
+export function multiSet(keyValues: [string, unknown][]): void;
+export type MultiSet = typeof multiSet;
+
+export function multiRemove(keys: string[]): void;
+export type MultiRemove = typeof multiRemove;
diff --git a/packages/loot-core/src/platform/server/asyncStorage/index.electron.ts b/packages/loot-core/src/platform/server/asyncStorage/index.electron.ts
index bbd325b2d4..7551acb07f 100644
--- a/packages/loot-core/src/platform/server/asyncStorage/index.electron.ts
+++ b/packages/loot-core/src/platform/server/asyncStorage/index.electron.ts
@@ -3,11 +3,13 @@ import { join } from 'path';
 
 import * as lootFs from '../fs';
 
+import * as T from '.';
+
 let getStorePath = () => join(lootFs.getDataDir(), 'global-store.json');
 let store;
 let persisted = true;
 
-export const init = function ({ persist = true } = {}) {
+export const init: T.Init = function ({ persist = true } = {}) {
   if (persist) {
     try {
       store = JSON.parse(fs.readFileSync(getStorePath(), 'utf8'));
@@ -36,23 +38,23 @@ function _saveStore() {
   }
 }
 
-export const getItem = function (key) {
+export const getItem: T.GetItem = function (key) {
   return new Promise(function (resolve) {
     return resolve(store[key]);
   });
 };
 
-export const setItem = function (key, value) {
+export const setItem: T.SetItem = function (key, value) {
   store[key] = value;
   return _saveStore();
 };
 
-export const removeItem = function (key) {
+export const removeItem: T.RemoveItem = function (key) {
   delete store[key];
   return _saveStore();
 };
 
-export const multiGet = function (keys) {
+export const multiGet: T.MultiGet = function (keys) {
   return new Promise(function (resolve) {
     return resolve(
       keys.map(function (key) {
@@ -62,14 +64,14 @@ export const multiGet = function (keys) {
   });
 };
 
-export const multiSet = function (keyValues) {
+export const multiSet: T.MultiSet = function (keyValues) {
   keyValues.forEach(function ([key, value]) {
     store[key] = value;
   });
   return _saveStore();
 };
 
-export const multiRemove = function (keys) {
+export const multiRemove: T.MultiRemove = function (keys) {
   keys.forEach(function (key) {
     delete store[key];
   });
diff --git a/packages/loot-core/src/platform/server/asyncStorage/index.testing.ts b/packages/loot-core/src/platform/server/asyncStorage/index.testing.ts
index 34f5182fa0..38fdc09180 100644
--- a/packages/loot-core/src/platform/server/asyncStorage/index.testing.ts
+++ b/packages/loot-core/src/platform/server/asyncStorage/index.testing.ts
@@ -1,22 +1,24 @@
+import * as T from '.';
+
 const store = {};
 
-export const init = function () {};
+export const init: T.Init = function () {};
 
-export const getItem = function (key) {
+export const getItem: T.GetItem = function (key) {
   return new Promise(function (resolve) {
     return resolve(store[key]);
   });
 };
 
-export const setItem = function (key, value) {
+export const setItem: T.SetItem = function (key, value) {
   store[key] = value;
 };
 
-export const removeItem = function (key) {
+export const removeItem: T.RemoveItem = function (key) {
   delete store[key];
 };
 
-export const multiGet = function (keys) {
+export const multiGet: T.MultiGet = function (keys) {
   return new Promise(function (resolve) {
     return resolve(
       keys.map(function (key) {
@@ -26,13 +28,13 @@ export const multiGet = function (keys) {
   });
 };
 
-export const multiSet = function (keyValues) {
+export const multiSet: T.MultiSet = function (keyValues) {
   keyValues.forEach(function ([key, value]) {
     store[key] = value;
   });
 };
 
-export const multiRemove = function (keys) {
+export const multiRemove: T.MultiRemove = function (keys) {
   keys.forEach(function (key) {
     delete store[key];
   });
diff --git a/packages/loot-core/src/platform/server/asyncStorage/index.web.ts b/packages/loot-core/src/platform/server/asyncStorage/index.web.ts
index 0cab70039c..e0bde31202 100644
--- a/packages/loot-core/src/platform/server/asyncStorage/index.web.ts
+++ b/packages/loot-core/src/platform/server/asyncStorage/index.web.ts
@@ -1,6 +1,8 @@
 import { getDatabase } from '../indexeddb';
 
-export const init = function () {};
+import * as T from '.';
+
+export const init: T.Init = function () {};
 
 function commit(trans) {
   if (trans.commit) {
@@ -8,7 +10,7 @@ function commit(trans) {
   }
 }
 
-export const getItem = async function (key) {
+export const getItem: T.GetItem = async function (key) {
   let db = await getDatabase();
 
   let transaction = db.transaction(['asyncStorage'], 'readonly');
@@ -22,7 +24,7 @@ export const getItem = async function (key) {
   });
 };
 
-export const setItem = async function (key, value) {
+export const setItem: T.SetItem = async function (key, value) {
   let db = await getDatabase();
 
   let transaction = db.transaction(['asyncStorage'], 'readwrite');
@@ -36,7 +38,7 @@ export const setItem = async function (key, value) {
   });
 };
 
-export const removeItem = async function (key) {
+export const removeItem: T.RemoveItem = async function (key) {
   let db = await getDatabase();
 
   let transaction = db.transaction(['asyncStorage'], 'readwrite');
@@ -50,7 +52,7 @@ export const removeItem = async function (key) {
   });
 };
 
-export const multiGet = async function (keys) {
+export const multiGet: T.MultiGet = async function (keys) {
   let db = await getDatabase();
 
   let transaction = db.transaction(['asyncStorage'], 'readonly');
@@ -58,7 +60,7 @@ export const multiGet = async function (keys) {
 
   let promise = Promise.all(
     keys.map(key => {
-      return new Promise((resolve, reject) => {
+      return new Promise<[string, unknown]>((resolve, reject) => {
         let req = objectStore.get(key);
         req.onerror = e => reject(e);
         req.onsuccess = e => resolve([key, e.target.result]);
@@ -70,7 +72,7 @@ export const multiGet = async function (keys) {
   return promise;
 };
 
-export const multiSet = async function (keyValues) {
+export const multiSet: T.MultiSet = async function (keyValues) {
   let db = await getDatabase();
 
   let transaction = db.transaction(['asyncStorage'], 'readwrite');
@@ -90,7 +92,7 @@ export const multiSet = async function (keyValues) {
   return promise;
 };
 
-export const multiRemove = async function (keys) {
+export const multiRemove: T.MultiRemove = async function (keys) {
   let db = await getDatabase();
 
   let transaction = db.transaction(['asyncStorage'], 'readwrite');
diff --git a/packages/loot-core/src/platform/server/fetch/index.d.ts b/packages/loot-core/src/platform/server/fetch/index.d.ts
index 5d610e61bd..67e3001dc4 100644
--- a/packages/loot-core/src/platform/server/fetch/index.d.ts
+++ b/packages/loot-core/src/platform/server/fetch/index.d.ts
@@ -1,4 +1,7 @@
-export function fetch(input: RequestInfo | URL): Promise<unknown>;
+export function fetch(
+  input: RequestInfo | URL,
+  options?: unknown,
+): Promise<Response>;
 export function fetchBinary(
   input: RequestInfo | URL,
   filepath: string,
diff --git a/packages/loot-core/src/platform/server/log/index.api.ts b/packages/loot-core/src/platform/server/log/index.api.ts
index 15f9a99164..cd368c8453 100644
--- a/packages/loot-core/src/platform/server/log/index.api.ts
+++ b/packages/loot-core/src/platform/server/log/index.api.ts
@@ -1,6 +1,6 @@
-import type Logger from '.';
+import type * as T from '.';
 
-const logger: Logger = {
+const logger: T.Logger = {
   info: (...args) => {
     console.log(...args);
   },
diff --git a/packages/loot-core/src/platform/server/log/index.d.ts b/packages/loot-core/src/platform/server/log/index.d.ts
index 6a08454159..00b23ca4db 100644
--- a/packages/loot-core/src/platform/server/log/index.d.ts
+++ b/packages/loot-core/src/platform/server/log/index.d.ts
@@ -1,9 +1,10 @@
 import { type Transports } from 'electron-log';
 
-interface Logger {
+export interface Logger {
   info(...args: unknown[]): void;
   warn(...args: unknown[]): void;
   transports?: Transports;
 }
 
-export default Logger;
+const logger: Logger;
+export default logger;
diff --git a/packages/loot-core/src/platform/server/log/index.electron.ts b/packages/loot-core/src/platform/server/log/index.electron.ts
index 7232b970bd..9aba4ec63f 100644
--- a/packages/loot-core/src/platform/server/log/index.electron.ts
+++ b/packages/loot-core/src/platform/server/log/index.electron.ts
@@ -1,6 +1,6 @@
 import logger from 'electron-log';
 
-import type Logger from '.';
+import type * as T from '.';
 
 if (logger.transports) {
   logger.transports.file.appName = 'Actual';
@@ -9,4 +9,4 @@ if (logger.transports) {
   logger.transports.console.level = false;
 }
 
-export default logger as Logger;
+export default logger as T.Logger;
diff --git a/packages/loot-core/src/platform/server/log/index.web.ts b/packages/loot-core/src/platform/server/log/index.web.ts
index 15f9a99164..cd368c8453 100644
--- a/packages/loot-core/src/platform/server/log/index.web.ts
+++ b/packages/loot-core/src/platform/server/log/index.web.ts
@@ -1,6 +1,6 @@
-import type Logger from '.';
+import type * as T from '.';
 
-const logger: Logger = {
+const logger: T.Logger = {
   info: (...args) => {
     console.log(...args);
   },
diff --git a/packages/loot-core/src/platform/server/sqlite/index.d.ts b/packages/loot-core/src/platform/server/sqlite/index.d.ts
index 0460c0113d..3c5821903a 100644
--- a/packages/loot-core/src/platform/server/sqlite/index.d.ts
+++ b/packages/loot-core/src/platform/server/sqlite/index.d.ts
@@ -1,3 +1,5 @@
+import { type Database } from 'better-sqlite3';
+
 export async function init(): unknown;
 
 export function _getModule(): SqlJsStatic;
@@ -7,15 +9,15 @@ export function prepare(db, sql): unknown;
 export function runQuery(
   db: unknown,
   sql: string,
-  params?: string[],
+  params?: (string | number)[],
   fetchAll?: false,
 ): { changes: unknown };
-export function runQuery(
+export function runQuery<T>(
   db: unknown,
   sql: string,
-  params: string[],
+  params: (string | number)[],
   fetchAll: true,
-): unknown[];
+): T[];
 
 export function execQuery(db, sql): void;
 
@@ -23,7 +25,7 @@ export function transaction(db, fn): unknown;
 
 export async function asyncTransaction(db, fn): unknown;
 
-export async function openDatabase(pathOrBuffer?: string | Buffer): unknown;
+export async function openDatabase(pathOrBuffer?: string | Buffer): Database;
 
 export function closeDatabase(db): void;
 
diff --git a/packages/loot-core/src/platform/server/sqlite/index.electron.ts b/packages/loot-core/src/platform/server/sqlite/index.electron.ts
index ac4224640e..7f03188dc3 100644
--- a/packages/loot-core/src/platform/server/sqlite/index.electron.ts
+++ b/packages/loot-core/src/platform/server/sqlite/index.electron.ts
@@ -87,10 +87,10 @@ export function openDatabase(pathOrBuffer) {
   let db = new Database(pathOrBuffer);
   // Define Unicode-aware LOWER and UPPER implementation.
   // This is necessary because better-sqlite3 uses SQLite build without ICU support.
-  db.function('UNICODE_LOWER', { deterministic: true }, arg =>
+  db.function('UNICODE_LOWER', { deterministic: true }, (arg: string | null) =>
     arg?.toLowerCase(),
   );
-  db.function('UNICODE_UPPER', { deterministic: true }, arg =>
+  db.function('UNICODE_UPPER', { deterministic: true }, (arg: string | null) =>
     arg?.toUpperCase(),
   );
   return db;
diff --git a/packages/loot-core/src/server/__mocks__/post.js b/packages/loot-core/src/server/__mocks__/post.ts
similarity index 100%
rename from packages/loot-core/src/server/__mocks__/post.js
rename to packages/loot-core/src/server/__mocks__/post.ts
diff --git a/packages/loot-core/src/server/accounts/__snapshots__/parse-file.test.js.snap b/packages/loot-core/src/server/accounts/__snapshots__/parse-file.test.ts.snap
similarity index 100%
rename from packages/loot-core/src/server/accounts/__snapshots__/parse-file.test.js.snap
rename to packages/loot-core/src/server/accounts/__snapshots__/parse-file.test.ts.snap
diff --git a/packages/loot-core/src/server/accounts/__snapshots__/sync.test.js.snap b/packages/loot-core/src/server/accounts/__snapshots__/sync.test.ts.snap
similarity index 100%
rename from packages/loot-core/src/server/accounts/__snapshots__/sync.test.js.snap
rename to packages/loot-core/src/server/accounts/__snapshots__/sync.test.ts.snap
diff --git a/packages/loot-core/src/server/accounts/__snapshots__/transaction-rules.test.js.snap b/packages/loot-core/src/server/accounts/__snapshots__/transaction-rules.test.ts.snap
similarity index 100%
rename from packages/loot-core/src/server/accounts/__snapshots__/transaction-rules.test.js.snap
rename to packages/loot-core/src/server/accounts/__snapshots__/transaction-rules.test.ts.snap
diff --git a/packages/loot-core/src/server/accounts/__snapshots__/transfer.test.js.snap b/packages/loot-core/src/server/accounts/__snapshots__/transfer.test.ts.snap
similarity index 100%
rename from packages/loot-core/src/server/accounts/__snapshots__/transfer.test.js.snap
rename to packages/loot-core/src/server/accounts/__snapshots__/transfer.test.ts.snap
diff --git a/packages/loot-core/src/server/accounts/export-to-csv.js b/packages/loot-core/src/server/accounts/export-to-csv.ts
similarity index 100%
rename from packages/loot-core/src/server/accounts/export-to-csv.js
rename to packages/loot-core/src/server/accounts/export-to-csv.ts
diff --git a/packages/loot-core/src/server/accounts/link.js b/packages/loot-core/src/server/accounts/link.ts
similarity index 100%
rename from packages/loot-core/src/server/accounts/link.js
rename to packages/loot-core/src/server/accounts/link.ts
diff --git a/packages/loot-core/src/server/accounts/parse-file.test.js b/packages/loot-core/src/server/accounts/parse-file.test.ts
similarity index 97%
rename from packages/loot-core/src/server/accounts/parse-file.test.js
rename to packages/loot-core/src/server/accounts/parse-file.test.ts
index cc86ac696a..a44754a165 100644
--- a/packages/loot-core/src/server/accounts/parse-file.test.js
+++ b/packages/loot-core/src/server/accounts/parse-file.test.ts
@@ -28,7 +28,11 @@ async function getTransactions(accountId) {
   );
 }
 
-async function importFileWithRealTime(accountId, filepath, dateFormat) {
+async function importFileWithRealTime(
+  accountId,
+  filepath,
+  dateFormat?: string,
+) {
   // Emscripten requires a real Date.now!
   global.restoreDateNow();
   let { errors, transactions } = await parseFile(filepath);
diff --git a/packages/loot-core/src/server/accounts/parse-file.js b/packages/loot-core/src/server/accounts/parse-file.ts
similarity index 94%
rename from packages/loot-core/src/server/accounts/parse-file.js
rename to packages/loot-core/src/server/accounts/parse-file.ts
index 9f2b8211ed..06e2ae8c19 100644
--- a/packages/loot-core/src/server/accounts/parse-file.js
+++ b/packages/loot-core/src/server/accounts/parse-file.ts
@@ -7,7 +7,7 @@ import { looselyParseAmount } from '../../shared/util';
 
 import qif2json from './qif2json';
 
-export function parseFile(filepath, options) {
+export function parseFile(filepath, options?: unknown) {
   let errors = [];
   let m = filepath.match(/\.[^.]*$/);
 
@@ -30,10 +30,10 @@ export function parseFile(filepath, options) {
     message: 'Invalid file type',
     internal: '',
   });
-  return { errors };
+  return { errors, transactions: undefined };
 }
 
-async function parseCSV(filepath, options = {}) {
+async function parseCSV(filepath, options: { delimiter?: string } = {}) {
   let errors = [];
   let contents = await fs.readFile(filepath);
 
@@ -148,6 +148,7 @@ async function parseOFX(filepath) {
       ofxParser: true,
       which: 'both',
       errors: {
+        length: oldErrors.length + newErrors.length,
         oldErrors,
         newErrors,
       },
@@ -157,6 +158,7 @@ async function parseOFX(filepath) {
       ofxParser: true,
       which: 'old',
       errors: {
+        length: oldErrors.length,
         oldErrors,
       },
       transactions: newTrans,
@@ -166,6 +168,7 @@ async function parseOFX(filepath) {
       ofxParser: true,
       which: 'new',
       errors: {
+        length: newErrors.length,
         newErrors,
       },
       transactions: oldTrans,
@@ -196,7 +199,7 @@ async function parseOfxJavascript(filepath) {
   // not sure about browser. We want latin1 and not utf8.
   // For some reason, utf8 does not parse ofx files correctly here.
   const contents = new TextDecoder('latin1').decode(
-    await fs.readFile(filepath, 'binary'),
+    (await fs.readFile(filepath, 'binary')) as Buffer,
   );
 
   let data;
diff --git a/packages/loot-core/src/server/accounts/payees.js b/packages/loot-core/src/server/accounts/payees.ts
similarity index 100%
rename from packages/loot-core/src/server/accounts/payees.js
rename to packages/loot-core/src/server/accounts/payees.ts
diff --git a/packages/loot-core/src/server/accounts/qif2json.js b/packages/loot-core/src/server/accounts/qif2json.ts
similarity index 66%
rename from packages/loot-core/src/server/accounts/qif2json.js
rename to packages/loot-core/src/server/accounts/qif2json.ts
index 1f0dc8892b..aff8e4c3d6 100644
--- a/packages/loot-core/src/server/accounts/qif2json.js
+++ b/packages/loot-core/src/server/accounts/qif2json.ts
@@ -1,19 +1,44 @@
-export default function parse(qif, options) {
-  var lines = qif.split('\n'),
-    line = lines.shift(),
-    type = /!Type:([^$]*)$/.exec(line.trim()),
-    data = {},
-    transactions = (data.transactions = []),
-    transaction = {};
+type Division = {
+  category?: string;
+  subcategory?: string;
+  description?: string;
+  amount?: number;
+};
 
-  options = options || {};
+type QIFTransaction = {
+  date?: string;
+  amount?: string;
+  number?: string;
+  memo?: string;
+  address?: string[];
+  clearedStatus?: string;
+  category?: string;
+  subcategory?: string;
+  payee?: string;
+  division?: Division[];
+};
+
+export default function parse(qif, options: { dateFormat?: string } = {}) {
+  let lines = qif.split('\n');
+  let line = lines.shift();
+  let type = /!Type:([^$]*)$/.exec(line.trim());
+  let data: {
+    dateFormat: string | undefined;
+    type?;
+    transactions: QIFTransaction[];
+  } = {
+    dateFormat: options.dateFormat,
+    transactions: [],
+  };
+  let transactions = data.transactions;
+  let transaction: QIFTransaction = {};
 
   if (!type || !type.length) {
     throw new Error('File does not appear to be a valid qif file: ' + line);
   }
   data.type = type[1];
 
-  var division = {};
+  let division: Division = {};
 
   while ((line = lines.shift())) {
     line = line.trim();
@@ -44,7 +69,7 @@ export default function parse(qif, options) {
         transaction.payee = line.substring(1).replace(/&amp;/g, '&');
         break;
       case 'L':
-        var lArray = line.substring(1).split(':');
+        let lArray = line.substring(1).split(':');
         transaction.category = lArray[0];
         if (lArray[1] !== undefined) {
           transaction.subcategory = lArray[1];
@@ -54,7 +79,7 @@ export default function parse(qif, options) {
         transaction.clearedStatus = line.substring(1);
         break;
       case 'S':
-        var sArray = line.substring(1).split(':');
+        let sArray = line.substring(1).split(':');
         division.category = sArray[0];
         if (sArray[1] !== undefined) {
           division.subcategory = sArray[1];
@@ -81,7 +106,5 @@ export default function parse(qif, options) {
   if (Object.keys(transaction).length) {
     transactions.push(transaction);
   }
-
-  data.dateFormat = options.dateFormat;
   return data;
 }
diff --git a/packages/loot-core/src/server/accounts/rules.test.js b/packages/loot-core/src/server/accounts/rules.test.ts
similarity index 100%
rename from packages/loot-core/src/server/accounts/rules.test.js
rename to packages/loot-core/src/server/accounts/rules.test.ts
diff --git a/packages/loot-core/src/server/accounts/rules.js b/packages/loot-core/src/server/accounts/rules.ts
similarity index 97%
rename from packages/loot-core/src/server/accounts/rules.js
rename to packages/loot-core/src/server/accounts/rules.ts
index 580b3e715d..37d547a0d7 100644
--- a/packages/loot-core/src/server/accounts/rules.js
+++ b/packages/loot-core/src/server/accounts/rules.ts
@@ -199,6 +199,14 @@ let CONDITION_TYPES = {
 };
 
 export class Condition {
+  field;
+  op;
+  options;
+  rawValue;
+  type;
+  unparsedValue;
+  value;
+
   constructor(op, field, value, options, fieldTypes) {
     let typeName = fieldTypes.get(field);
     assert(typeName, 'internal', 'Invalid condition field: ' + field);
@@ -393,6 +401,13 @@ export class Condition {
 let ACTION_OPS = ['set', 'link-schedule'];
 
 export class Action {
+  field;
+  op;
+  options;
+  rawValue;
+  type;
+  value;
+
   constructor(op, field, value, options, fieldTypes) {
     assert(
       ACTION_OPS.includes(op),
@@ -440,7 +455,27 @@ export class Action {
 }
 
 export class Rule {
-  constructor({ id, stage, conditionsOp, conditions, actions, fieldTypes }) {
+  actions;
+  conditions;
+  conditionsOp;
+  id;
+  stage;
+
+  constructor({
+    id,
+    stage,
+    conditionsOp,
+    conditions,
+    actions,
+    fieldTypes,
+  }: {
+    id?: string;
+    stage?;
+    conditionsOp;
+    conditions;
+    actions;
+    fieldTypes;
+  }) {
     this.id = id;
     this.stage = stage;
     this.conditionsOp = conditionsOp;
@@ -498,7 +533,11 @@ export class Rule {
 }
 
 export class RuleIndexer {
-  constructor({ field, method }) {
+  field;
+  method;
+  rules;
+
+  constructor({ field, method }: { field: string; method?: string }) {
     this.field = field;
     this.method = method;
     this.rules = new Map();
diff --git a/packages/loot-core/src/server/accounts/sync.test.js b/packages/loot-core/src/server/accounts/sync.test.ts
similarity index 97%
rename from packages/loot-core/src/server/accounts/sync.test.js
rename to packages/loot-core/src/server/accounts/sync.test.ts
index 56e22d3dfa..aedd21a910 100644
--- a/packages/loot-core/src/server/accounts/sync.test.js
+++ b/packages/loot-core/src/server/accounts/sync.test.ts
@@ -19,8 +19,17 @@ import * as transfer from './transfer';
 const papaJohns = 'Papa Johns east side';
 const lowes = 'Lowe’s Store';
 
+jest.mock('../../shared/months', () => ({
+  ...jest.requireActual('../../shared/months'),
+  currentDay: jest.fn(),
+  currentMonth: jest.fn(),
+}));
+
 beforeEach(async () => {
   mockSyncServer.reset();
+  jest.resetAllMocks();
+  (monthUtils.currentDay as jest.Mock).mockReturnValue('2017-10-15');
+  (monthUtils.currentMonth as jest.Mock).mockReturnValue('2017-10');
   await global.emptyDatabase()();
   await loadMappings();
   await loadRules();
@@ -103,7 +112,6 @@ async function getAllPayees() {
 
 describe('Account sync', () => {
   test('reconcile creates payees correctly', async () => {
-    monthUtils.currentDay = () => '2017-10-15';
     let { id } = await prepareDatabase();
 
     let payees = await getAllPayees();
@@ -128,7 +136,6 @@ describe('Account sync', () => {
   });
 
   test('reconcile matches single transaction', async () => {
-    monthUtils.currentDay = () => '2017-10-15';
     let mockTransactions = prepMockTransactions();
     const { id, account_id } = await prepareDatabase();
 
@@ -166,7 +173,6 @@ describe('Account sync', () => {
   });
 
   test('reconcile matches multiple transactions', async () => {
-    monthUtils.currentDay = () => '2017-10-15';
     let mockTransactions = prepMockTransactions();
     const { id, account_id } = await prepareDatabase();
 
@@ -231,7 +237,6 @@ describe('Account sync', () => {
   });
 
   test('reconcile matches multiple transactions (imported_id wins)', async () => {
-    monthUtils.currentDay = () => '2017-10-15';
     let mockTransactions = prepMockTransactions();
     const { id, account_id } = await prepareDatabase();
 
@@ -277,7 +282,6 @@ describe('Account sync', () => {
   });
 
   test('import never matches existing with financial ids', async () => {
-    monthUtils.currentDay = () => '2017-10-15';
     let mockTransactions = prepMockTransactions();
     const { id, account_id } = await prepareDatabase();
 
@@ -312,14 +316,13 @@ describe('Account sync', () => {
 
     differ.expectToMatchDiff(await getAllTransactions());
 
-    monthUtils.currentDay = () => '2017-10-17';
+    (monthUtils.currentDay as jest.Mock).mockReturnValue('2017-10-17');
     await syncAccount('userId', 'userKey', id, account_id, 'bank');
 
     differ.expectToMatchDiff(await getAllTransactions());
   });
 
   test('import updates transfers when matched', async () => {
-    monthUtils.currentDay = () => '2017-10-15';
     let mockTransactions = prepMockTransactions();
     const { id, account_id } = await prepareDatabase();
     await db.insertAccount({ id: 'two', name: 'two' });
@@ -347,7 +350,7 @@ describe('Account sync', () => {
 
     differ.expectToMatchDiff(await getAllTransactions());
 
-    monthUtils.currentDay = () => '2017-10-17';
+    (monthUtils.currentDay as jest.Mock).mockReturnValue('2017-10-17');
     await syncAccount('userId', 'userKey', id, account_id, 'bank');
 
     // Don't use `differ.expectToMatchDiff` because there's too many
@@ -607,16 +610,13 @@ describe('Account sync', () => {
   });
 
   test('imports transactions for current day and adds latest', async () => {
-    monthUtils.currentDay = () => '2017-10-15';
-    monthUtils.currentMonth = () => '2017-10';
-
     const { id, account_id } = await prepareDatabase();
 
     expect((await getAllTransactions()).length).toBe(0);
     await syncAccount('userId', 'userKey', id, account_id, 'bank');
     expect(await getAllTransactions()).toMatchSnapshot();
 
-    monthUtils.currentDay = () => '2017-10-17';
+    (monthUtils.currentDay as jest.Mock).mockReturnValue('2017-10-17');
 
     await syncAccount('userId', 'userKey', id, account_id, 'bank');
     expect(await getAllTransactions()).toMatchSnapshot();
diff --git a/packages/loot-core/src/server/accounts/sync.js b/packages/loot-core/src/server/accounts/sync.ts
similarity index 99%
rename from packages/loot-core/src/server/accounts/sync.js
rename to packages/loot-core/src/server/accounts/sync.ts
index 1f3b872234..4eaef2aa89 100644
--- a/packages/loot-core/src/server/accounts/sync.js
+++ b/packages/loot-core/src/server/accounts/sync.ts
@@ -116,7 +116,7 @@ async function downloadTransactions(
   acctId,
   bankId,
   since,
-  count,
+  count?: number,
 ) {
   let allTransactions = [];
   let accountBalance = null;
@@ -180,7 +180,6 @@ async function downloadNordigenTransactions(
   acctId,
   bankId,
   since,
-  count,
 ) {
   let userToken = await asyncStorage.getItem('user-token');
   if (userToken) {
@@ -213,7 +212,7 @@ async function downloadNordigenTransactions(
 
     return {
       transactions: booked,
-      accountBalances: balances,
+      accountBalance: balances,
       startingBalance,
     };
   }
@@ -243,7 +242,7 @@ async function resolvePayee(trans, payeeName, payeesToCreate) {
 async function normalizeTransactions(
   transactions,
   acctId,
-  { rawPayeeName } = {},
+  { rawPayeeName = false } = {},
 ) {
   let payeesToCreate = new Map();
 
diff --git a/packages/loot-core/src/server/accounts/transaction-rules.test.js b/packages/loot-core/src/server/accounts/transaction-rules.test.ts
similarity index 100%
rename from packages/loot-core/src/server/accounts/transaction-rules.test.js
rename to packages/loot-core/src/server/accounts/transaction-rules.test.ts
diff --git a/packages/loot-core/src/server/accounts/transaction-rules.js b/packages/loot-core/src/server/accounts/transaction-rules.ts
similarity index 99%
rename from packages/loot-core/src/server/accounts/transaction-rules.js
rename to packages/loot-core/src/server/accounts/transaction-rules.ts
index a317adc05d..d1f3602cc4 100644
--- a/packages/loot-core/src/server/accounts/transaction-rules.js
+++ b/packages/loot-core/src/server/accounts/transaction-rules.ts
@@ -78,7 +78,7 @@ function toInternalField(obj) {
 }
 
 export const ruleModel = {
-  validate(rule, { update } = {}) {
+  validate(rule, { update }: { update?: boolean } = {}) {
     requiredFields('rules', rule, ['conditions', 'actions'], update);
 
     if (!update || 'stage' in rule) {
@@ -513,7 +513,7 @@ function* getIsSetterRules(
   stage,
   condField,
   actionField,
-  { condValue, actionValue },
+  { condValue, actionValue }: { condValue?: string; actionValue?: string },
 ) {
   let rules = getRules();
   for (let i = 0; i < rules.length; i++) {
@@ -541,7 +541,7 @@ function* getOneOfSetterRules(
   stage,
   condField,
   actionField,
-  { condValue, actionValue },
+  { condValue, actionValue }: { condValue?: string; actionValue: string },
 ) {
   let rules = getRules();
   for (let i = 0; i < rules.length; i++) {
diff --git a/packages/loot-core/src/server/accounts/transactions.js b/packages/loot-core/src/server/accounts/transactions.ts
similarity index 92%
rename from packages/loot-core/src/server/accounts/transactions.js
rename to packages/loot-core/src/server/accounts/transactions.ts
index 348c7342f1..2775825eb0 100644
--- a/packages/loot-core/src/server/accounts/transactions.js
+++ b/packages/loot-core/src/server/accounts/transactions.ts
@@ -6,7 +6,7 @@ import { batchMessages } from '../sync';
 import * as rules from './transaction-rules';
 import * as transfer from './transfer';
 
-async function idsWithChildren(ids) {
+async function idsWithChildren(ids: string[]) {
   let whereIds = whereIn(ids, 'parent_id');
   let rows = await db.all(
     `SELECT id FROM v_transactions_internal WHERE ${whereIds}`,
@@ -18,7 +18,7 @@ async function idsWithChildren(ids) {
   return [...set];
 }
 
-async function getTransactionsByIds(ids) {
+async function getTransactionsByIds(ids: string[]) {
   // TODO: convert to whereIn
   //
   // or better yet, use ActualQL
@@ -37,6 +37,17 @@ export async function batchUpdateTransactions({
   updated,
   learnCategories = false,
   detectOrphanPayees = true,
+}: {
+  added?: Array<{ id: string; payee: unknown; category: unknown }>;
+  deleted?: Array<{ id: string; payee: unknown }>;
+  updated?: Array<{
+    id: string;
+    payee: unknown;
+    account: unknown;
+    category: unknown;
+  }>;
+  learnCategories?: boolean;
+  detectOrphanPayees?: boolean;
 }) {
   // Track the ids of each type of transaction change (see below for why)
   let addedIds = [];
diff --git a/packages/loot-core/src/server/accounts/transfer.test.js b/packages/loot-core/src/server/accounts/transfer.test.ts
similarity index 94%
rename from packages/loot-core/src/server/accounts/transfer.test.js
rename to packages/loot-core/src/server/accounts/transfer.test.ts
index 98a0360970..5788a301c7 100644
--- a/packages/loot-core/src/server/accounts/transfer.test.js
+++ b/packages/loot-core/src/server/accounts/transfer.test.ts
@@ -34,11 +34,22 @@ async function prepareDatabase() {
   });
 }
 
+type Transaction = {
+  account: string;
+  amount: number;
+  category?: string;
+  date: string;
+  id?: string;
+  notes?: string;
+  payee: string;
+  transfer_id?: string;
+};
+
 describe('Transfer', () => {
   test('transfers are properly inserted/updated/deleted', async () => {
     await prepareDatabase();
 
-    let transaction = {
+    let transaction: Transaction = {
       account: 'one',
       amount: 5000,
       payee: await db.insertPayee({ name: 'Non-transfer' }),
@@ -126,7 +137,7 @@ describe('Transfer', () => {
       "SELECT * FROM payees WHERE transfer_acct = 'three'",
     );
 
-    let transaction = {
+    let transaction: Transaction = {
       account: 'one',
       amount: 5000,
       payee: await db.insertPayee({ name: 'Non-transfer' }),
diff --git a/packages/loot-core/src/server/accounts/transfer.js b/packages/loot-core/src/server/accounts/transfer.ts
similarity index 100%
rename from packages/loot-core/src/server/accounts/transfer.js
rename to packages/loot-core/src/server/accounts/transfer.ts
diff --git a/packages/loot-core/src/server/aql/compiler.test.js b/packages/loot-core/src/server/aql/compiler.test.ts
similarity index 100%
rename from packages/loot-core/src/server/aql/compiler.test.js
rename to packages/loot-core/src/server/aql/compiler.test.ts
diff --git a/packages/loot-core/src/server/aql/compiler.js b/packages/loot-core/src/server/aql/compiler.ts
similarity index 97%
rename from packages/loot-core/src/server/aql/compiler.js
rename to packages/loot-core/src/server/aql/compiler.ts
index fce92d9ebe..ddd858b05e 100644
--- a/packages/loot-core/src/server/aql/compiler.js
+++ b/packages/loot-core/src/server/aql/compiler.ts
@@ -324,7 +324,7 @@ function castInput(state, expr, type) {
 }
 
 // TODO: remove state from these functions
-function val(state, expr, type) {
+function val(state, expr, type?: string) {
   let castedExpr = expr;
 
   // Cast the type if necessary
@@ -347,11 +347,11 @@ function val(state, expr, type) {
   return castedExpr.value;
 }
 
-function valArray(state, arr, types) {
+function valArray(state, arr: unknown[], types?: string[]) {
   return arr.map((value, idx) => val(state, value, types ? types[idx] : null));
 }
 
-function validateArgLength(arr, min, max) {
+function validateArgLength(arr: unknown[], min: number, max?: number) {
   if (max == null) {
     max = min;
   }
@@ -931,7 +931,7 @@ function isAggregateFunction(expr) {
     return true;
   }
 
-  return !!argExprs.find(ex => isAggregateFunction(ex));
+  return !!(argExprs as unknown[]).find(ex => isAggregateFunction(ex));
 }
 
 export function isAggregateQuery(queryState) {
@@ -952,7 +952,16 @@ export function isAggregateQuery(queryState) {
   });
 }
 
-export function compileQuery(queryState, schema, schemaConfig = {}) {
+type SchemaConfig = {
+  tableViews?: Record<string, unknown> | ((...args: unknown[]) => unknown);
+  tableFilters?: (name: string) => unknown[];
+  customizeQuery?: <T>(queryString: T) => T;
+};
+export function compileQuery(
+  queryState,
+  schema,
+  schemaConfig: SchemaConfig = {},
+) {
   let { withDead, validateRefs = true, tableOptions, rawMode } = queryState;
 
   let {
@@ -979,7 +988,7 @@ export function compileQuery(queryState, schema, schemaConfig = {}) {
     return filters;
   };
 
-  let tableRef = (name, isJoin) => {
+  let tableRef = (name: string, isJoin?: boolean) => {
     let view =
       typeof tableViews === 'function'
         ? tableViews(name, { withDead, isJoin, tableOptions })
@@ -1101,7 +1110,11 @@ export function defaultConstructQuery(queryState, state, sqlPieces) {
   `;
 }
 
-export function generateSQLWithState(queryState, schema, schemaConfig) {
+export function generateSQLWithState(
+  queryState,
+  schema?: unknown,
+  schemaConfig?: unknown,
+) {
   let { sqlPieces, state } = compileQuery(queryState, schema, schemaConfig);
   return { sql: defaultConstructQuery(queryState, state, sqlPieces), state };
 }
diff --git a/packages/loot-core/src/server/aql/exec.test.js b/packages/loot-core/src/server/aql/exec.test.ts
similarity index 99%
rename from packages/loot-core/src/server/aql/exec.test.js
rename to packages/loot-core/src/server/aql/exec.test.ts
index 78cb4730c3..1bcbbbdd03 100644
--- a/packages/loot-core/src/server/aql/exec.test.js
+++ b/packages/loot-core/src/server/aql/exec.test.ts
@@ -16,7 +16,7 @@ function repeat(arr, times) {
   return result;
 }
 
-function runQuery(query, options) {
+function runQuery(query, options?: unknown) {
   return aql.runQuery(schema, schemaConfig, query, options);
 }
 
diff --git a/packages/loot-core/src/server/aql/exec.js b/packages/loot-core/src/server/aql/exec.ts
similarity index 100%
rename from packages/loot-core/src/server/aql/exec.js
rename to packages/loot-core/src/server/aql/exec.ts
diff --git a/packages/loot-core/src/server/aql/index.js b/packages/loot-core/src/server/aql/index.ts
similarity index 100%
rename from packages/loot-core/src/server/aql/index.js
rename to packages/loot-core/src/server/aql/index.ts
diff --git a/packages/loot-core/src/server/aql/schema-helpers.test.js b/packages/loot-core/src/server/aql/schema-helpers.test.ts
similarity index 100%
rename from packages/loot-core/src/server/aql/schema-helpers.test.js
rename to packages/loot-core/src/server/aql/schema-helpers.test.ts
diff --git a/packages/loot-core/src/server/aql/schema-helpers.js b/packages/loot-core/src/server/aql/schema-helpers.ts
similarity index 98%
rename from packages/loot-core/src/server/aql/schema-helpers.js
rename to packages/loot-core/src/server/aql/schema-helpers.ts
index 72737d433c..33dd90f7ed 100644
--- a/packages/loot-core/src/server/aql/schema-helpers.js
+++ b/packages/loot-core/src/server/aql/schema-helpers.ts
@@ -84,7 +84,13 @@ export function convertOutputType(value, type) {
   return value;
 }
 
-export function conform(schema, schemaConfig, table, obj, { skipNull } = {}) {
+export function conform(
+  schema,
+  schemaConfig,
+  table,
+  obj,
+  { skipNull = false } = {},
+) {
   let tableSchema = schema[table];
   if (tableSchema == null) {
     throw new Error(`Table “${table}” does not exist`);
diff --git a/packages/loot-core/src/server/aql/schema/run-query.ts b/packages/loot-core/src/server/aql/schema/run-query.ts
index f8088f56b1..403315bd8f 100644
--- a/packages/loot-core/src/server/aql/schema/run-query.ts
+++ b/packages/loot-core/src/server/aql/schema/run-query.ts
@@ -8,7 +8,7 @@ import { schemaExecutors } from './executors';
 
 import { schema, schemaConfig } from './index';
 
-export function runCompiledQuery(query, sqlPieces, state, params) {
+export function runCompiledQuery(query, sqlPieces, state, params?: unknown) {
   return _runCompiledQuery(query, sqlPieces, state, {
     params,
     executors: schemaExecutors,
diff --git a/packages/loot-core/src/server/aql/views.test.js b/packages/loot-core/src/server/aql/views.test.ts
similarity index 100%
rename from packages/loot-core/src/server/aql/views.test.js
rename to packages/loot-core/src/server/aql/views.test.ts
diff --git a/packages/loot-core/src/server/aql/views.js b/packages/loot-core/src/server/aql/views.ts
similarity index 100%
rename from packages/loot-core/src/server/aql/views.js
rename to packages/loot-core/src/server/aql/views.ts
diff --git a/packages/loot-core/src/server/budget/actions.js b/packages/loot-core/src/server/budget/actions.ts
similarity index 100%
rename from packages/loot-core/src/server/budget/actions.js
rename to packages/loot-core/src/server/budget/actions.ts
diff --git a/packages/loot-core/src/server/budget/app.js b/packages/loot-core/src/server/budget/app.ts
similarity index 100%
rename from packages/loot-core/src/server/budget/app.js
rename to packages/loot-core/src/server/budget/app.ts
diff --git a/packages/loot-core/src/server/budget/base.test.js b/packages/loot-core/src/server/budget/base.test.ts
similarity index 100%
rename from packages/loot-core/src/server/budget/base.test.js
rename to packages/loot-core/src/server/budget/base.test.ts
diff --git a/packages/loot-core/src/server/budget/base.js b/packages/loot-core/src/server/budget/base.ts
similarity index 95%
rename from packages/loot-core/src/server/budget/base.js
rename to packages/loot-core/src/server/budget/base.ts
index 9b5c454289..3489be3f22 100644
--- a/packages/loot-core/src/server/budget/base.js
+++ b/packages/loot-core/src/server/budget/base.ts
@@ -95,7 +95,7 @@ function handleAccountChange(months, oldValue, newValue) {
     );
 
     months.forEach(month => {
-      let sheetName = monthUtils.sheetForMonth(month, getBudgetType());
+      let sheetName = monthUtils.sheetForMonth(month);
 
       rows.forEach(row => {
         sheet
@@ -118,7 +118,7 @@ function handleTransactionChange(transaction, changedFields) {
     transaction.category
   ) {
     let month = monthUtils.monthFromDate(db.fromDateRepr(transaction.date));
-    let sheetName = monthUtils.sheetForMonth(month, getBudgetType());
+    let sheetName = monthUtils.sheetForMonth(month);
 
     sheet
       .get()
@@ -128,7 +128,7 @@ function handleTransactionChange(transaction, changedFields) {
 
 function handleCategoryMappingChange(months, oldValue, newValue) {
   months.forEach(month => {
-    let sheetName = monthUtils.sheetForMonth(month, getBudgetType());
+    let sheetName = monthUtils.sheetForMonth(month);
     if (oldValue) {
       sheet
         .get()
@@ -197,8 +197,8 @@ function handleCategoryChange(months, oldValue, newValue) {
 
     months.forEach(month => {
       let prevMonth = monthUtils.prevMonth(month);
-      let prevSheetName = monthUtils.sheetForMonth(prevMonth, budgetType);
-      let sheetName = monthUtils.sheetForMonth(month, budgetType);
+      let prevSheetName = monthUtils.sheetForMonth(prevMonth);
+      let sheetName = monthUtils.sheetForMonth(month);
       let { start, end } = monthUtils.bounds(month);
 
       createCategory(newValue, sheetName, prevSheetName, start, end);
@@ -222,7 +222,7 @@ function handleCategoryChange(months, oldValue, newValue) {
     let id = newValue.id;
 
     months.forEach(month => {
-      let sheetName = monthUtils.sheetForMonth(month, budgetType);
+      let sheetName = monthUtils.sheetForMonth(month);
       removeDeps(sheetName, oldValue.cat_group, id);
       addDeps(sheetName, newValue.cat_group, id);
     });
@@ -271,7 +271,7 @@ function handleCategoryGroupChange(months, oldValue, newValue) {
   if (newValue.tombstone === 1 && oldValue && oldValue.tombstone === 0) {
     let id = newValue.id;
     months.forEach(month => {
-      let sheetName = monthUtils.sheetForMonth(month, budgetType);
+      let sheetName = monthUtils.sheetForMonth(month);
       removeDeps(sheetName, id);
     });
   } else if (
@@ -282,7 +282,7 @@ function handleCategoryGroupChange(months, oldValue, newValue) {
 
     if (!group.is_income || budgetType !== 'rollover') {
       months.forEach(month => {
-        let sheetName = monthUtils.sheetForMonth(month, budgetType);
+        let sheetName = monthUtils.sheetForMonth(month);
 
         // Dirty, dirty hack. These functions should not be async, but this is
         // OK because we're leveraging the sync nature of queries. Ideally we
@@ -402,8 +402,8 @@ export async function createBudget(months) {
     if (!meta.createdMonths.has(month)) {
       let prevMonth = monthUtils.prevMonth(month);
       let { start, end } = monthUtils.bounds(month);
-      let sheetName = monthUtils.sheetForMonth(month, budgetType);
-      let prevSheetName = monthUtils.sheetForMonth(prevMonth, budgetType);
+      let sheetName = monthUtils.sheetForMonth(month);
+      let prevSheetName = monthUtils.sheetForMonth(prevMonth);
 
       categories.forEach(cat => {
         createCategory(cat, sheetName, prevSheetName, start, end);
diff --git a/packages/loot-core/src/server/budget/goaltemplates.js b/packages/loot-core/src/server/budget/goaltemplates.ts
similarity index 100%
rename from packages/loot-core/src/server/budget/goaltemplates.js
rename to packages/loot-core/src/server/budget/goaltemplates.ts
diff --git a/packages/loot-core/src/server/budget/report.js b/packages/loot-core/src/server/budget/report.ts
similarity index 100%
rename from packages/loot-core/src/server/budget/report.js
rename to packages/loot-core/src/server/budget/report.ts
diff --git a/packages/loot-core/src/server/budget/rollover.js b/packages/loot-core/src/server/budget/rollover.ts
similarity index 98%
rename from packages/loot-core/src/server/budget/rollover.js
rename to packages/loot-core/src/server/budget/rollover.ts
index 1c8080a0a9..20b3c60faa 100644
--- a/packages/loot-core/src/server/budget/rollover.js
+++ b/packages/loot-core/src/server/budget/rollover.ts
@@ -7,7 +7,7 @@ import { number, sumAmounts, flatten2, unflatten2 } from './util';
 
 function getBlankSheet(months) {
   let blankMonth = monthUtils.prevMonth(months[0]);
-  return monthUtils.sheetForMonth(blankMonth, 'rollover');
+  return monthUtils.sheetForMonth(blankMonth);
 }
 
 export function createBlankCategory(cat, months) {
diff --git a/packages/loot-core/src/server/budget/types/handlers.d.ts b/packages/loot-core/src/server/budget/types/handlers.d.ts
new file mode 100644
index 0000000000..c41294e4f6
--- /dev/null
+++ b/packages/loot-core/src/server/budget/types/handlers.d.ts
@@ -0,0 +1,25 @@
+export interface BudgetHandlers {
+  'budget/budget-amount': (...args: unknown[]) => Promise<unknown>;
+
+  'budget/copy-previous-month': (...args: unknown[]) => Promise<unknown>;
+
+  'budget/set-zero': (...args: unknown[]) => Promise<unknown>;
+
+  'budget/set-3month-avg': (...args: unknown[]) => Promise<unknown>;
+
+  'budget/apply-goal-template': (...args: unknown[]) => Promise<unknown>;
+
+  'budget/overwrite-goal-template': (...args: unknown[]) => Promise<unknown>;
+
+  'budget/hold-for-next-month': (...args: unknown[]) => Promise<unknown>;
+
+  'budget/reset-hold': (...args: unknown[]) => Promise<unknown>;
+
+  'budget/cover-overspending': (...args: unknown[]) => Promise<unknown>;
+
+  'budget/transfer-available': (...args: unknown[]) => Promise<unknown>;
+
+  'budget/transfer-category': (...args: unknown[]) => Promise<unknown>;
+
+  'budget/set-carryover': (...args: unknown[]) => Promise<unknown>;
+}
diff --git a/packages/loot-core/src/server/budget/util.js b/packages/loot-core/src/server/budget/util.ts
similarity index 100%
rename from packages/loot-core/src/server/budget/util.js
rename to packages/loot-core/src/server/budget/util.ts
diff --git a/packages/loot-core/src/server/crdt/__snapshots__/merkle.test.js.snap b/packages/loot-core/src/server/crdt/__snapshots__/merkle.test.ts.snap
similarity index 100%
rename from packages/loot-core/src/server/crdt/__snapshots__/merkle.test.js.snap
rename to packages/loot-core/src/server/crdt/__snapshots__/merkle.test.ts.snap
diff --git a/packages/loot-core/src/server/crdt/index.js b/packages/loot-core/src/server/crdt/index.ts
similarity index 100%
rename from packages/loot-core/src/server/crdt/index.js
rename to packages/loot-core/src/server/crdt/index.ts
diff --git a/packages/loot-core/src/server/crdt/merkle.test.js b/packages/loot-core/src/server/crdt/merkle.test.ts
similarity index 98%
rename from packages/loot-core/src/server/crdt/merkle.test.js
rename to packages/loot-core/src/server/crdt/merkle.test.ts
index 91b383cddc..cf7828a1b7 100644
--- a/packages/loot-core/src/server/crdt/merkle.test.js
+++ b/packages/loot-core/src/server/crdt/merkle.test.ts
@@ -28,8 +28,8 @@ describe('merkle trie', () => {
   });
 
   test('diff returns the correct time difference', () => {
-    let trie1 = {};
-    let trie2 = {};
+    let trie1: { hash?: unknown } = {};
+    let trie2: { hash?: unknown } = {};
 
     const messages = [
       // First client messages
@@ -90,7 +90,7 @@ describe('merkle trie', () => {
       message('2018-11-01T02:37:00.000Z-0000-0123456789ABCDEF', 2100),
     ];
 
-    let trie = {};
+    let trie: { hash?: unknown } = {};
     messages.forEach(msg => {
       trie = merkle.insert(trie, msg.timestamp);
     });
diff --git a/packages/loot-core/src/server/crdt/merkle.js b/packages/loot-core/src/server/crdt/merkle.ts
similarity index 100%
rename from packages/loot-core/src/server/crdt/merkle.js
rename to packages/loot-core/src/server/crdt/merkle.ts
diff --git a/packages/loot-core/src/server/crdt/timestamp.test.js b/packages/loot-core/src/server/crdt/timestamp.test.ts
similarity index 96%
rename from packages/loot-core/src/server/crdt/timestamp.test.js
rename to packages/loot-core/src/server/crdt/timestamp.test.ts
index 2ed80bf6e2..5dde3525ef 100644
--- a/packages/loot-core/src/server/crdt/timestamp.test.js
+++ b/packages/loot-core/src/server/crdt/timestamp.test.ts
@@ -2,15 +2,16 @@ import { Timestamp } from './timestamp';
 
 describe('Timestamp', function () {
   let now = 0;
+  let prevNow;
 
   beforeEach(function () {
-    Date.prevNow = Date.now;
+    prevNow = Date.now;
     Date.now = () => now;
     Timestamp.init({ node: '1' });
   });
 
   afterEach(() => {
-    Date.now = Date.prevNow;
+    Date.now = prevNow;
   });
 
   describe('comparison', function () {
@@ -24,7 +25,7 @@ describe('Timestamp', function () {
 
   describe('parsing', function () {
     it('should not parse', function () {
-      var invalidInputs = [
+      let invalidInputs = [
         null,
         undefined,
         {},
@@ -40,19 +41,19 @@ describe('Timestamp', function () {
         '9999-12-31T23:59:59.999Z-10000-FFFFFFFFFFFFFFFF',
         '9999-12-31T23:59:59.999Z-FFFF-10000000000000000',
       ];
-      for (var invalidInput of invalidInputs) {
+      for (let invalidInput of invalidInputs) {
         expect(Timestamp.parse(invalidInput)).toBe(null);
       }
     });
 
     it('should parse', function () {
-      var validInputs = [
+      let validInputs = [
         '1970-01-01T00:00:00.000Z-0000-0000000000000000',
         '2015-04-24T22:23:42.123Z-1000-0123456789ABCDEF',
         '9999-12-31T23:59:59.999Z-FFFF-FFFFFFFFFFFFFFFF',
       ];
-      for (var validInput of validInputs) {
-        var parsed = Timestamp.parse(validInput);
+      for (let validInput of validInputs) {
+        let parsed = Timestamp.parse(validInput);
         expect(typeof parsed).toBe('object');
         expect(parsed.millis() >= 0).toBeTruthy();
         expect(parsed.millis() < 253402300800000).toBeTruthy();
@@ -117,7 +118,7 @@ describe('Timestamp', function () {
 
     it('should fail with counter overflow', function () {
       now = 40;
-      for (var i = 0; i < 65536; i++) Timestamp.send();
+      for (let i = 0; i < 65536; i++) Timestamp.send();
       expect(Timestamp.send).toThrow(Timestamp.OverflowError);
     });
 
diff --git a/packages/loot-core/src/server/crdt/timestamp.js b/packages/loot-core/src/server/crdt/timestamp.ts
similarity index 83%
rename from packages/loot-core/src/server/crdt/timestamp.js
rename to packages/loot-core/src/server/crdt/timestamp.ts
index ddcbaaf5fc..5b25656095 100644
--- a/packages/loot-core/src/server/crdt/timestamp.js
+++ b/packages/loot-core/src/server/crdt/timestamp.ts
@@ -68,7 +68,7 @@ export function makeClientId() {
   return uuid.v4Sync().replace(/-/g, '').slice(-16);
 }
 
-var config = {
+let config = {
   // Allow 5 minutes of clock drift
   maxDrift: 5 * 60 * 1000,
 };
@@ -80,7 +80,20 @@ const MAX_NODE_LENGTH = 16;
  * timestamp instance class
  */
 export class Timestamp {
-  constructor(millis, counter, node) {
+  static init;
+  static max;
+  static parse;
+  static recv;
+  static send;
+  static since;
+  static zero;
+  static ClockDriftError;
+  static DuplicateNodeError;
+  static OverflowError;
+
+  _state;
+
+  constructor(millis: number, counter: number, node: string) {
     this._state = {
       millis: millis,
       counter: counter,
@@ -118,6 +131,8 @@ export class Timestamp {
 }
 
 class MutableTimestamp extends Timestamp {
+  static from;
+
   setMillis(n) {
     this._state.millis = n;
   }
@@ -142,7 +157,7 @@ MutableTimestamp.from = timestamp => {
 // Timestamp generator initialization
 // * sets the node ID to an arbitrary value
 // * useful for mocking/unit testing
-Timestamp.init = function (options = {}) {
+Timestamp.init = function (options: { maxDrift?: number; node?: string } = {}) {
   if (options.maxDrift) {
     config.maxDrift = options.maxDrift;
   }
@@ -157,7 +172,6 @@ Timestamp.init = function (options = {}) {
           : '',
       ),
     ),
-    null,
   );
 };
 
@@ -171,17 +185,17 @@ Timestamp.send = function () {
   }
 
   // retrieve the local wall time
-  var phys = Date.now();
+  let phys = Date.now();
 
   // unpack the clock.timestamp logical time and counter
-  var lOld = clock.timestamp.millis();
-  var cOld = clock.timestamp.counter();
+  let lOld = clock.timestamp.millis();
+  let cOld = clock.timestamp.counter();
 
   // calculate the next logical time and counter
   // * ensure that the logical time never goes backward
   // * increment the counter if phys time does not advance
-  var lNew = Math.max(lOld, phys);
-  var cNew = lOld === lNew ? cOld + 1 : 0;
+  let lNew = Math.max(lOld, phys);
+  let cNew = lOld === lNew ? cOld + 1 : 0;
 
   // check the result for drift and counter overflow
   if (lNew - phys > config.maxDrift) {
@@ -211,11 +225,11 @@ Timestamp.recv = function (msg) {
   }
 
   // retrieve the local wall time
-  var phys = Date.now();
+  let phys = Date.now();
 
   // unpack the message wall time/counter
-  var lMsg = msg.millis();
-  var cMsg = msg.counter();
+  let lMsg = msg.millis();
+  let cMsg = msg.counter();
 
   // assert the node id and remote clock drift
   // if (msg.node() === clock.timestamp.node()) {
@@ -226,8 +240,8 @@ Timestamp.recv = function (msg) {
   }
 
   // unpack the clock.timestamp logical time and counter
-  var lOld = clock.timestamp.millis();
-  var cOld = clock.timestamp.counter();
+  let lOld = clock.timestamp.millis();
+  let cOld = clock.timestamp.counter();
 
   // calculate the next logical time and counter
   // . ensure that the logical time never goes backward
@@ -235,8 +249,8 @@ Timestamp.recv = function (msg) {
   // . if max = old > message, increment local counter
   // . if max = messsage > old, increment message counter
   // . otherwise, clocks are monotonic, reset counter
-  var lNew = Math.max(Math.max(lOld, phys), lMsg);
-  var cNew =
+  let lNew = Math.max(Math.max(lOld, phys), lMsg);
+  let cNew =
     lNew === lOld && lNew === lMsg
       ? Math.max(cOld, cMsg) + 1
       : lNew === lOld
@@ -270,11 +284,11 @@ Timestamp.recv = function (msg) {
  */
 Timestamp.parse = function (timestamp) {
   if (typeof timestamp === 'string') {
-    var parts = timestamp.split('-');
+    let parts = timestamp.split('-');
     if (parts && parts.length === 5) {
-      var millis = Date.parse(parts.slice(0, 3).join('-')).valueOf();
-      var counter = parseInt(parts[3], 16);
-      var node = parts[4];
+      let millis = Date.parse(parts.slice(0, 3).join('-')).valueOf();
+      let counter = parseInt(parts[3], 16);
+      let node = parts[4];
       if (
         !isNaN(millis) &&
         millis >= 0 &&
@@ -293,7 +307,7 @@ Timestamp.parse = function (timestamp) {
 /**
  * zero/minimum timestamp
  */
-var zero = Timestamp.parse('1970-01-01T00:00:00.000Z-0000-0000000000000000');
+let zero = Timestamp.parse('1970-01-01T00:00:00.000Z-0000-0000000000000000');
 Timestamp.zero = function () {
   return zero;
 };
@@ -301,7 +315,7 @@ Timestamp.zero = function () {
 /**
  * maximum timestamp
  */
-var max = Timestamp.parse('9999-12-31T23:59:59.999Z-FFFF-FFFFFFFFFFFFFFFF');
+let max = Timestamp.parse('9999-12-31T23:59:59.999Z-FFFF-FFFFFFFFFFFFFFFF');
 Timestamp.max = function () {
   return max;
 };
@@ -315,24 +329,21 @@ Timestamp.since = isoString => {
  */
 Timestamp.DuplicateNodeError = class extends Error {
   constructor(node) {
-    super();
-    this.type = 'DuplicateNodeError';
-    this.message = 'duplicate node identifier ' + node;
+    super('duplicate node identifier ' + node);
+    this.name = 'DuplicateNodeError';
   }
 };
 
 Timestamp.ClockDriftError = class extends Error {
   constructor(...args) {
-    super();
-    this.type = 'ClockDriftError';
-    this.message = ['maximum clock drift exceeded'].concat(args).join(' ');
+    super(['maximum clock drift exceeded'].concat(args).join(' '));
+    this.name = 'ClockDriftError';
   }
 };
 
 Timestamp.OverflowError = class extends Error {
   constructor() {
-    super();
-    this.type = 'OverflowError';
-    this.message = 'timestamp counter overflow';
+    super('timestamp counter overflow');
+    this.name = 'OverflowError';
   }
 };
diff --git a/packages/loot-core/src/server/db/__snapshots__/index.test.js.snap b/packages/loot-core/src/server/db/__snapshots__/index.test.ts.snap
similarity index 100%
rename from packages/loot-core/src/server/db/__snapshots__/index.test.js.snap
rename to packages/loot-core/src/server/db/__snapshots__/index.test.ts.snap
diff --git a/packages/loot-core/src/server/db/index.test.js b/packages/loot-core/src/server/db/index.test.ts
similarity index 100%
rename from packages/loot-core/src/server/db/index.test.js
rename to packages/loot-core/src/server/db/index.test.ts
diff --git a/packages/loot-core/src/server/db/index.ts b/packages/loot-core/src/server/db/index.ts
index e67eedfcba..46eef23109 100644
--- a/packages/loot-core/src/server/db/index.ts
+++ b/packages/loot-core/src/server/db/index.ts
@@ -143,18 +143,18 @@ export function asyncTransaction(fn) {
 // This function is marked as async because `runQuery` is no longer
 // async. We return a promise here until we've audited all the code to
 // make sure nothing calls `.then` on this.
-export async function all(sql, params?: string[]) {
+export async function all(sql, params?: (string | number)[]) {
   return runQuery(sql, params, true);
 }
 
-export async function first(sql, params?: string[]) {
+export async function first(sql, params?: (string | number)[]) {
   const arr = await runQuery(sql, params, true);
   return arr.length === 0 ? null : arr[0];
 }
 
 // The underlying sql system is now sync, but we can't update `first` yet
 // without auditing all uses of it
-export function firstSync(sql, params?: string[]) {
+export function firstSync(sql, params?: (string | number)[]) {
   const arr = runQuery(sql, params, true);
   return arr.length === 0 ? null : arr[0];
 }
@@ -162,7 +162,7 @@ export function firstSync(sql, params?: string[]) {
 // This function is marked as async because `runQuery` is no longer
 // async. We return a promise here until we've audited all the code to
 // make sure nothing calls `.then` on this.
-export async function run(sql, params?: string[]) {
+export async function run(sql, params?: (string | number)[]) {
   return runQuery(sql, params);
 }
 
@@ -328,7 +328,7 @@ export async function moveCategoryGroup(id, targetId) {
   await update('category_groups', { id, sort_order });
 }
 
-export async function deleteCategoryGroup(group, transferId) {
+export async function deleteCategoryGroup(group, transferId?: string) {
   const categories = await all('SELECT * FROM categories WHERE cat_group = ?', [
     group.id,
   ]);
@@ -387,7 +387,7 @@ export function updateCategory(category) {
   return update('categories', category);
 }
 
-export async function moveCategory(id, groupId, targetId) {
+export async function moveCategory(id, groupId, targetId?: string) {
   if (!groupId) {
     throw new Error('moveCategory: groupId is required');
   }
@@ -404,7 +404,7 @@ export async function moveCategory(id, groupId, targetId) {
   await update('categories', { id, sort_order, cat_group: groupId });
 }
 
-export async function deleteCategory(category, transferId) {
+export async function deleteCategory(category, transferId?: string) {
   if (transferId) {
     // We need to update all the deleted categories that currently
     // point to the one we're about to delete so they all are
@@ -634,7 +634,7 @@ export async function getTransactionsByDate(
   throw new Error('`getTransactionsByDate` is deprecated');
 }
 
-export async function getTransactions(accountId, arg2) {
+export async function getTransactions(accountId, arg2?: unknown) {
   if (arg2 !== undefined) {
     throw new Error(
       '`getTransactions` was given a second argument, it now only takes a single argument `accountId`',
diff --git a/packages/loot-core/src/server/db/mappings.js b/packages/loot-core/src/server/db/mappings.ts
similarity index 100%
rename from packages/loot-core/src/server/db/mappings.js
rename to packages/loot-core/src/server/db/mappings.ts
diff --git a/packages/loot-core/src/server/db/sort.js b/packages/loot-core/src/server/db/sort.ts
similarity index 96%
rename from packages/loot-core/src/server/db/sort.js
rename to packages/loot-core/src/server/db/sort.ts
index 7106b74a57..c033c1f17c 100644
--- a/packages/loot-core/src/server/db/sort.js
+++ b/packages/loot-core/src/server/db/sort.ts
@@ -13,7 +13,7 @@ function midpoint(items, to) {
   }
 }
 
-export function shoveSortOrders(items, targetId) {
+export function shoveSortOrders(items, targetId?: string) {
   const to = items.findIndex(item => item.id === targetId);
   const target = items[to];
   const before = items[to - 1];
diff --git a/packages/loot-core/src/server/db/util.js b/packages/loot-core/src/server/db/util.ts
similarity index 93%
rename from packages/loot-core/src/server/db/util.js
rename to packages/loot-core/src/server/db/util.ts
index 5cae87332f..72e6b704f7 100644
--- a/packages/loot-core/src/server/db/util.js
+++ b/packages/loot-core/src/server/db/util.ts
@@ -25,7 +25,7 @@ export async function incrFetch(
   return results;
 }
 
-export function whereIn(ids, field) {
+export function whereIn(ids: string[], field: string) {
   let ids2 = [...new Set(ids)];
   // eslint-disable-next-line rulesdir/typography
   let filter = `${field} IN (` + ids2.map(id => `'${id}'`).join(',') + ')';
diff --git a/packages/loot-core/src/server/migrate/__snapshots__/migrations.test.js.snap b/packages/loot-core/src/server/migrate/__snapshots__/migrations.test.ts.snap
similarity index 100%
rename from packages/loot-core/src/server/migrate/__snapshots__/migrations.test.js.snap
rename to packages/loot-core/src/server/migrate/__snapshots__/migrations.test.ts.snap
diff --git a/packages/loot-core/src/server/migrate/cli.js b/packages/loot-core/src/server/migrate/cli.ts
similarity index 95%
rename from packages/loot-core/src/server/migrate/cli.js
rename to packages/loot-core/src/server/migrate/cli.ts
index 5f67f773c9..75cdf303c6 100755
--- a/packages/loot-core/src/server/migrate/cli.js
+++ b/packages/loot-core/src/server/migrate/cli.ts
@@ -33,7 +33,7 @@ const argv = require('yargs').options({
   },
 }).argv;
 
-function getDatabase(shouldReset) {
+function getDatabase() {
   return sqlite.openDatabase(argv.db);
 }
 
@@ -47,7 +47,7 @@ function create(migrationName) {
 
 async function list(db) {
   const migrationsDir = getMigrationsDir();
-  const applied = await getAppliedMigrations(getDatabase(), migrationsDir);
+  const applied = await getAppliedMigrations(getDatabase());
   const all = await getMigrationList(migrationsDir);
   const pending = getPending(applied, all);
 
diff --git a/packages/loot-core/src/server/migrate/migrations.test.js b/packages/loot-core/src/server/migrate/migrations.test.ts
similarity index 100%
rename from packages/loot-core/src/server/migrate/migrations.test.js
rename to packages/loot-core/src/server/migrate/migrations.test.ts
diff --git a/packages/loot-core/src/server/migrate/migrations.js b/packages/loot-core/src/server/migrate/migrations.ts
similarity index 98%
rename from packages/loot-core/src/server/migrate/migrations.js
rename to packages/loot-core/src/server/migrate/migrations.ts
index 231b8be28b..898ff0fd6e 100644
--- a/packages/loot-core/src/server/migrate/migrations.js
+++ b/packages/loot-core/src/server/migrate/migrations.ts
@@ -36,7 +36,7 @@ export function getUpMigration(id, names) {
 }
 
 export async function getAppliedMigrations(db) {
-  const rows = await sqlite.runQuery(
+  const rows = await sqlite.runQuery<{ id: number }>(
     db,
     'SELECT * FROM __migrations__ ORDER BY id ASC',
     [],
diff --git a/packages/loot-core/src/server/notes/app.js b/packages/loot-core/src/server/notes/app.ts
similarity index 100%
rename from packages/loot-core/src/server/notes/app.js
rename to packages/loot-core/src/server/notes/app.ts
diff --git a/packages/loot-core/src/server/notes/types/handlers.d.ts b/packages/loot-core/src/server/notes/types/handlers.d.ts
new file mode 100644
index 0000000000..873a7fb12b
--- /dev/null
+++ b/packages/loot-core/src/server/notes/types/handlers.d.ts
@@ -0,0 +1,3 @@
+export interface NoteHandlers {
+  'notes-save': (arg: { id; note }) => Promise<unknown>;
+}
diff --git a/packages/loot-core/src/server/post.js b/packages/loot-core/src/server/post.ts
similarity index 100%
rename from packages/loot-core/src/server/post.js
rename to packages/loot-core/src/server/post.ts
diff --git a/packages/loot-core/src/server/schedules/app.test.js b/packages/loot-core/src/server/schedules/app.test.ts
similarity index 100%
rename from packages/loot-core/src/server/schedules/app.test.js
rename to packages/loot-core/src/server/schedules/app.test.ts
diff --git a/packages/loot-core/src/server/schedules/app.js b/packages/loot-core/src/server/schedules/app.ts
similarity index 97%
rename from packages/loot-core/src/server/schedules/app.js
rename to packages/loot-core/src/server/schedules/app.ts
index dce9170f84..962a9be5fa 100644
--- a/packages/loot-core/src/server/schedules/app.js
+++ b/packages/loot-core/src/server/schedules/app.ts
@@ -126,7 +126,17 @@ export async function fixRuleForSchedule(id) {
   return getRules().find(rule => rule.id === newId);
 }
 
-export async function setNextDate({ id, start, conditions, reset }) {
+export async function setNextDate({
+  id,
+  start,
+  conditions,
+  reset,
+}: {
+  id: string;
+  start?;
+  conditions?;
+  reset?: boolean;
+}) {
   if (conditions == null) {
     let rule = await getRuleForSchedule(id);
     if (rule == null) {
@@ -190,7 +200,10 @@ export async function checkIfScheduleExists(name, scheduleId) {
   return true;
 }
 
-export async function createSchedule({ schedule, conditions = [] } = {}) {
+export async function createSchedule({
+  schedule = null,
+  conditions = [],
+} = {}) {
   let scheduleId = (schedule && schedule.id) || uuid.v4Sync();
 
   let { date: dateCond } = extractScheduleConds(conditions);
@@ -242,7 +255,15 @@ export async function createSchedule({ schedule, conditions = [] } = {}) {
 
 // TODO: don't allow deleting rules that link schedules
 
-export async function updateSchedule({ schedule, conditions, resetNextDate }) {
+export async function updateSchedule({
+  schedule,
+  conditions,
+  resetNextDate,
+}: {
+  schedule;
+  conditions?;
+  resetNextDate?: boolean;
+}) {
   if (schedule.rule) {
     throw new Error('You cannot change the rule of a schedule');
   }
diff --git a/packages/loot-core/src/server/schedules/find-schedules.js b/packages/loot-core/src/server/schedules/find-schedules.ts
similarity index 99%
rename from packages/loot-core/src/server/schedules/find-schedules.js
rename to packages/loot-core/src/server/schedules/find-schedules.ts
index 656579e974..d812cf2457 100644
--- a/packages/loot-core/src/server/schedules/find-schedules.js
+++ b/packages/loot-core/src/server/schedules/find-schedules.ts
@@ -107,7 +107,7 @@ async function schedulesForPattern(
   numDays,
   baseConfig,
   accountId,
-  partialMatchRank,
+  partialMatchRank?: number,
 ) {
   let schedules = [];
 
diff --git a/packages/loot-core/src/server/schedules/types/handlers.ts b/packages/loot-core/src/server/schedules/types/handlers.ts
new file mode 100644
index 0000000000..7f7ec60d6f
--- /dev/null
+++ b/packages/loot-core/src/server/schedules/types/handlers.ts
@@ -0,0 +1,19 @@
+export interface SchedulesHandlers {
+  'schedule/create': () => Promise<unknown>;
+
+  'schedule/update': () => Promise<unknown>;
+
+  'schedule/delete': () => Promise<unknown>;
+
+  'schedule/skip-next-date': () => Promise<unknown>;
+
+  'schedule/post-transaction': () => Promise<unknown>;
+
+  'schedule/force-run-service': () => Promise<unknown>;
+
+  'schedule/get-possible-transactions': () => Promise<unknown>;
+
+  'schedule/discover': () => Promise<unknown>;
+
+  'schedule/get-upcoming-dates': () => Promise<unknown>;
+}
diff --git a/packages/loot-core/src/server/spreadsheet/__snapshots__/spreadsheet.test.js.snap b/packages/loot-core/src/server/spreadsheet/__snapshots__/spreadsheet.test.ts.snap
similarity index 100%
rename from packages/loot-core/src/server/spreadsheet/__snapshots__/spreadsheet.test.js.snap
rename to packages/loot-core/src/server/spreadsheet/__snapshots__/spreadsheet.test.ts.snap
diff --git a/packages/loot-core/src/server/spreadsheet/globals.js b/packages/loot-core/src/server/spreadsheet/globals.ts
similarity index 100%
rename from packages/loot-core/src/server/spreadsheet/globals.js
rename to packages/loot-core/src/server/spreadsheet/globals.ts
diff --git a/packages/loot-core/src/server/spreadsheet/graph-data-structure.js b/packages/loot-core/src/server/spreadsheet/graph-data-structure.ts
similarity index 96%
rename from packages/loot-core/src/server/spreadsheet/graph-data-structure.js
rename to packages/loot-core/src/server/spreadsheet/graph-data-structure.ts
index 8f45dfdc2c..b4e4ee9a1a 100644
--- a/packages/loot-core/src/server/spreadsheet/graph-data-structure.js
+++ b/packages/loot-core/src/server/spreadsheet/graph-data-structure.ts
@@ -1,5 +1,5 @@
-function Graph(serialized) {
-  var graph = {
+function Graph() {
+  let graph = {
     addNode,
     removeNode,
     adjacent,
@@ -12,8 +12,8 @@ function Graph(serialized) {
     getEdges,
   };
 
-  var edges = new Map();
-  var incomingEdges = new Map();
+  let edges = new Map();
+  let incomingEdges = new Map();
 
   function getEdges() {
     return { edges, incomingEdges };
diff --git a/packages/loot-core/src/server/spreadsheet/spreadsheet.test.js b/packages/loot-core/src/server/spreadsheet/spreadsheet.test.ts
similarity index 98%
rename from packages/loot-core/src/server/spreadsheet/spreadsheet.test.js
rename to packages/loot-core/src/server/spreadsheet/spreadsheet.test.ts
index 33ed0b70bf..381444eb0c 100644
--- a/packages/loot-core/src/server/spreadsheet/spreadsheet.test.js
+++ b/packages/loot-core/src/server/spreadsheet/spreadsheet.test.ts
@@ -119,7 +119,7 @@ describe('Spreadsheet', () => {
     return new Promise(resolve => {
       spreadsheet.onFinish(() => {
         expect(spreadsheet.getValue('g!foo')).toMatchSnapshot();
-        resolve();
+        resolve(undefined);
       });
     });
   });
@@ -138,7 +138,7 @@ describe('Spreadsheet', () => {
     return new Promise(resolve => {
       spreadsheet.onFinish(() => {
         expect(spreadsheet.getValue('g!foo')).toMatchSnapshot();
-        resolve();
+        resolve(undefined);
       });
     });
   });
diff --git a/packages/loot-core/src/server/spreadsheet/spreadsheet.js b/packages/loot-core/src/server/spreadsheet/spreadsheet.ts
similarity index 96%
rename from packages/loot-core/src/server/spreadsheet/spreadsheet.js
rename to packages/loot-core/src/server/spreadsheet/spreadsheet.ts
index 9538f4a5e8..cab8611065 100644
--- a/packages/loot-core/src/server/spreadsheet/spreadsheet.js
+++ b/packages/loot-core/src/server/spreadsheet/spreadsheet.ts
@@ -6,7 +6,20 @@ import Graph from './graph-data-structure';
 import { unresolveName, resolveName } from './util';
 
 export default class Spreadsheet {
-  constructor(saveCache, setCacheStatus) {
+  _meta;
+  cacheBarrier;
+  computeQueue;
+  dirtyCells;
+  events;
+  graph;
+  nodes;
+  running;
+  saveCache;
+  setCacheStatus;
+  transactionDepth;
+
+  constructor(saveCache?: unknown, setCacheStatus?: unknown) {
+    // @ts-expect-error Graph should be converted to class
     this.graph = new Graph();
     this.nodes = new Map();
     this.transactionDepth = 0;
@@ -338,7 +351,7 @@ export default class Spreadsheet {
   createDynamic(
     sheetName,
     cellName,
-    { dependencies = [], run, initialValue, refresh },
+    { dependencies = [], run, initialValue, refresh = false },
   ) {
     let name = resolveName(sheetName, cellName);
     let node = this._getNode(name);
diff --git a/packages/loot-core/src/server/spreadsheet/sqlinterp.test.js b/packages/loot-core/src/server/spreadsheet/sqlinterp.test.ts
similarity index 100%
rename from packages/loot-core/src/server/spreadsheet/sqlinterp.test.js
rename to packages/loot-core/src/server/spreadsheet/sqlinterp.test.ts
diff --git a/packages/loot-core/src/server/spreadsheet/sqlinterp.js b/packages/loot-core/src/server/spreadsheet/sqlinterp.ts
similarity index 99%
rename from packages/loot-core/src/server/spreadsheet/sqlinterp.js
rename to packages/loot-core/src/server/spreadsheet/sqlinterp.ts
index d1ac4d5ca2..b30fa98475 100644
--- a/packages/loot-core/src/server/spreadsheet/sqlinterp.js
+++ b/packages/loot-core/src/server/spreadsheet/sqlinterp.ts
@@ -12,7 +12,7 @@ function bind(args, func) {
   // if (shouldLog) {
   //   console.log(args, func.toString());
   // }
-  for (var i = 0; i < args.length; i++) {
+  for (let i = 0; i < args.length; i++) {
     if (args[i] === AlwaysTrue) {
       return AlwaysTrue;
     }
diff --git a/packages/loot-core/src/server/spreadsheet/util.js b/packages/loot-core/src/server/spreadsheet/util.ts
similarity index 100%
rename from packages/loot-core/src/server/spreadsheet/util.js
rename to packages/loot-core/src/server/spreadsheet/util.ts
diff --git a/packages/loot-core/src/server/sync/README.md b/packages/loot-core/src/server/sync/README.md
index 5df92100ca..d9f4c17be7 100644
--- a/packages/loot-core/src/server/sync/README.md
+++ b/packages/loot-core/src/server/sync/README.md
@@ -11,9 +11,14 @@ This can be installed by downloading one of the [pre-built binaries](https://git
 Once installed, the protobuf can be generated by running the below commands.
 
 ```bash
-cd packages/loot-core/src/server/sync
+cd packages/loot-core
 
-protoc sync.proto --js_out=import_style=commonjs,binary:proto
+protoc --plugin="protoc-gen-ts=../../node_modules/.bin/protoc-gen-ts" \
+    --ts_opt=esModuleInterop=true \
+    --ts_out="src/server/sync/proto" \
+    --js_out=import_style=commonjs,binary:src/server/sync/proto \
+    --proto_path=src/server/sync \
+    sync.proto
 ```
 
 However there is one very important thing to remember! The default output includes this near the top:
diff --git a/packages/loot-core/src/server/sync/__snapshots__/sync.test.js.snap b/packages/loot-core/src/server/sync/__snapshots__/sync.test.ts.snap
similarity index 100%
rename from packages/loot-core/src/server/sync/__snapshots__/sync.test.js.snap
rename to packages/loot-core/src/server/sync/__snapshots__/sync.test.ts.snap
diff --git a/packages/loot-core/src/server/sync/encoder.js b/packages/loot-core/src/server/sync/encoder.ts
similarity index 95%
rename from packages/loot-core/src/server/sync/encoder.js
rename to packages/loot-core/src/server/sync/encoder.ts
index b64aa4d800..46e933e9b3 100644
--- a/packages/loot-core/src/server/sync/encoder.js
+++ b/packages/loot-core/src/server/sync/encoder.ts
@@ -80,7 +80,7 @@ export async function decode(data) {
 
     if (encrypted) {
       let binary = SyncPb.EncryptedData.deserializeBinary(
-        envelopePb.getContent(),
+        envelopePb.getContent() as Uint8Array,
       );
 
       let decrypted;
@@ -100,7 +100,9 @@ export async function decode(data) {
 
       msg = SyncPb.Message.deserializeBinary(decrypted);
     } else {
-      msg = SyncPb.Message.deserializeBinary(envelopePb.getContent());
+      msg = SyncPb.Message.deserializeBinary(
+        envelopePb.getContent() as Uint8Array,
+      );
     }
 
     messages.push({
diff --git a/packages/loot-core/src/server/sync/index.js b/packages/loot-core/src/server/sync/index.ts
similarity index 98%
rename from packages/loot-core/src/server/sync/index.js
rename to packages/loot-core/src/server/sync/index.ts
index 70023e05f9..104a6b97e6 100644
--- a/packages/loot-core/src/server/sync/index.js
+++ b/packages/loot-core/src/server/sync/index.ts
@@ -68,7 +68,7 @@ export function checkSyncingMode(mode) {
   }
 }
 
-function apply(msg, prev) {
+function apply(msg, prev?: unknown) {
   let { dataset, row, column, value } = msg;
 
   if (dataset === 'prefs') {
@@ -238,7 +238,16 @@ function applyMessagesForImport(messages) {
   });
 }
 
-export const applyMessages = sequential(async messages => {
+type Message = {
+  column: string;
+  dataset: string;
+  old?: unknown;
+  row: string;
+  timestamp: number;
+  value: unknown;
+};
+
+export const applyMessages = sequential(async (messages: Message[]) => {
   if (checkSyncingMode('import')) {
     return applyMessagesForImport(messages);
   } else if (checkSyncingMode('enabled')) {
@@ -287,7 +296,7 @@ export const applyMessages = sequential(async messages => {
     return data;
   }
 
-  let prefsToSet = {};
+  let prefsToSet: Record<string, unknown> = {};
   let oldData = await fetchData();
 
   undo.appendMessages(messages, oldData);
@@ -404,7 +413,7 @@ export const applyMessages = sequential(async messages => {
   return messages;
 });
 
-export function receiveMessages(messages) {
+export function receiveMessages(messages: Message[]) {
   messages.forEach(msg => {
     Timestamp.recv(msg.timestamp);
   });
@@ -662,7 +671,7 @@ async function _fullSync(sinceTimestamp, count, prevDiffTime) {
   let localTimeChanged = getClock().timestamp.toString() !== currentTime;
 
   // Apply the new messages
-  let receivedMessages = [];
+  let receivedMessages: unknown[] = [];
   if (res.messages.length > 0) {
     receivedMessages = await receiveMessages(
       res.messages.map(msg => ({
diff --git a/packages/loot-core/src/server/sync/make-test-message.js b/packages/loot-core/src/server/sync/make-test-message.ts
similarity index 100%
rename from packages/loot-core/src/server/sync/make-test-message.js
rename to packages/loot-core/src/server/sync/make-test-message.ts
diff --git a/packages/loot-core/src/server/sync/migrate.test.js b/packages/loot-core/src/server/sync/migrate.test.ts
similarity index 97%
rename from packages/loot-core/src/server/sync/migrate.test.js
rename to packages/loot-core/src/server/sync/migrate.test.ts
index 93810f8cba..58a1173804 100644
--- a/packages/loot-core/src/server/sync/migrate.test.js
+++ b/packages/loot-core/src/server/sync/migrate.test.ts
@@ -103,11 +103,7 @@ describe('sync migrations', () => {
           await sendMessages(msgs);
           await tracer.expect('applied');
 
-          let transactions = await db.all(
-            'SELECT * FROM transactions',
-            [],
-            true,
-          );
+          let transactions = await db.all('SELECT * FROM transactions', []);
           for (let trans of transactions) {
             let transMsgs = msgs
               .filter(msg => msg.row === trans.id)
diff --git a/packages/loot-core/src/server/sync/migrate.js b/packages/loot-core/src/server/sync/migrate.ts
similarity index 100%
rename from packages/loot-core/src/server/sync/migrate.js
rename to packages/loot-core/src/server/sync/migrate.ts
diff --git a/packages/loot-core/src/server/sync/proto/sync_pb.d.ts b/packages/loot-core/src/server/sync/proto/sync_pb.d.ts
new file mode 100644
index 0000000000..5a31387bf1
--- /dev/null
+++ b/packages/loot-core/src/server/sync/proto/sync_pb.d.ts
@@ -0,0 +1,206 @@
+// package:
+// file: sync.proto
+
+import * as jspb from 'google-protobuf';
+
+export class EncryptedData extends jspb.Message {
+  getIv(): Uint8Array | string;
+  getIv_asU8(): Uint8Array;
+  getIv_asB64(): string;
+  setIv(value: Uint8Array | string): void;
+
+  getAuthtag(): Uint8Array | string;
+  getAuthtag_asU8(): Uint8Array;
+  getAuthtag_asB64(): string;
+  setAuthtag(value: Uint8Array | string): void;
+
+  getData(): Uint8Array | string;
+  getData_asU8(): Uint8Array;
+  getData_asB64(): string;
+  setData(value: Uint8Array | string): void;
+
+  serializeBinary(): Uint8Array;
+  toObject(includeInstance?: boolean): EncryptedDataAsObject;
+  static toObject(
+    includeInstance: boolean,
+    msg: EncryptedData,
+  ): EncryptedDataAsObject;
+  static extensions: { [key: number]: jspb.ExtensionFieldInfo<jspb.Message> };
+  static extensionsBinary: {
+    [key: number]: jspb.ExtensionFieldBinaryInfo<jspb.Message>;
+  };
+  static serializeBinaryToWriter(
+    message: EncryptedData,
+    writer: jspb.BinaryWriter,
+  ): void;
+  static deserializeBinary(bytes: Uint8Array): EncryptedData;
+  static deserializeBinaryFromReader(
+    message: EncryptedData,
+    reader: jspb.BinaryReader,
+  ): EncryptedData;
+}
+
+export type EncryptedDataAsObject = {
+  iv: Uint8Array | string;
+  authtag: Uint8Array | string;
+  data: Uint8Array | string;
+};
+
+export class Message extends jspb.Message {
+  getDataset(): string;
+  setDataset(value: string): void;
+
+  getRow(): string;
+  setRow(value: string): void;
+
+  getColumn(): string;
+  setColumn(value: string): void;
+
+  getValue(): string;
+  setValue(value: string): void;
+
+  serializeBinary(): Uint8Array;
+  toObject(includeInstance?: boolean): MessageAsObject;
+  static toObject(includeInstance: boolean, msg: Message): MessageAsObject;
+  static extensions: { [key: number]: jspb.ExtensionFieldInfo<jspb.Message> };
+  static extensionsBinary: {
+    [key: number]: jspb.ExtensionFieldBinaryInfo<jspb.Message>;
+  };
+  static serializeBinaryToWriter(
+    message: Message,
+    writer: jspb.BinaryWriter,
+  ): void;
+  static deserializeBinary(bytes: Uint8Array): Message;
+  static deserializeBinaryFromReader(
+    message: Message,
+    reader: jspb.BinaryReader,
+  ): Message;
+}
+
+export type MessageAsObject = {
+  dataset: string;
+  row: string;
+  column: string;
+  value: string;
+};
+
+export class MessageEnvelope extends jspb.Message {
+  getTimestamp(): string;
+  setTimestamp(value: string): void;
+
+  getIsencrypted(): boolean;
+  setIsencrypted(value: boolean): void;
+
+  getContent(): Uint8Array | string;
+  getContent_asU8(): Uint8Array;
+  getContent_asB64(): string;
+  setContent(value: Uint8Array | string): void;
+
+  serializeBinary(): Uint8Array;
+  toObject(includeInstance?: boolean): MessageEnvelopeAsObject;
+  static toObject(
+    includeInstance: boolean,
+    msg: MessageEnvelope,
+  ): MessageEnvelopeAsObject;
+  static extensions: { [key: number]: jspb.ExtensionFieldInfo<jspb.Message> };
+  static extensionsBinary: {
+    [key: number]: jspb.ExtensionFieldBinaryInfo<jspb.Message>;
+  };
+  static serializeBinaryToWriter(
+    message: MessageEnvelope,
+    writer: jspb.BinaryWriter,
+  ): void;
+  static deserializeBinary(bytes: Uint8Array): MessageEnvelope;
+  static deserializeBinaryFromReader(
+    message: MessageEnvelope,
+    reader: jspb.BinaryReader,
+  ): MessageEnvelope;
+}
+
+export type MessageEnvelopeAsObject = {
+  timestamp: string;
+  isencrypted: boolean;
+  content: Uint8Array | string;
+};
+
+export class SyncRequest extends jspb.Message {
+  clearMessagesList(): void;
+  getMessagesList(): Array<MessageEnvelope>;
+  setMessagesList(value: Array<MessageEnvelope>): void;
+  addMessages(value?: MessageEnvelope, index?: number): MessageEnvelope;
+
+  getFileid(): string;
+  setFileid(value: string): void;
+
+  getGroupid(): string;
+  setGroupid(value: string): void;
+
+  getKeyid(): string;
+  setKeyid(value: string): void;
+
+  getSince(): string;
+  setSince(value: string): void;
+
+  serializeBinary(): Uint8Array;
+  toObject(includeInstance?: boolean): SyncRequestAsObject;
+  static toObject(
+    includeInstance: boolean,
+    msg: SyncRequest,
+  ): SyncRequestAsObject;
+  static extensions: { [key: number]: jspb.ExtensionFieldInfo<jspb.Message> };
+  static extensionsBinary: {
+    [key: number]: jspb.ExtensionFieldBinaryInfo<jspb.Message>;
+  };
+  static serializeBinaryToWriter(
+    message: SyncRequest,
+    writer: jspb.BinaryWriter,
+  ): void;
+  static deserializeBinary(bytes: Uint8Array): SyncRequest;
+  static deserializeBinaryFromReader(
+    message: SyncRequest,
+    reader: jspb.BinaryReader,
+  ): SyncRequest;
+}
+
+export type SyncRequestAsObject = {
+  messagesList: Array<MessageEnvelopeAsObject>;
+  fileid: string;
+  groupid: string;
+  keyid: string;
+  since: string;
+};
+
+export class SyncResponse extends jspb.Message {
+  clearMessagesList(): void;
+  getMessagesList(): Array<MessageEnvelope>;
+  setMessagesList(value: Array<MessageEnvelope>): void;
+  addMessages(value?: MessageEnvelope, index?: number): MessageEnvelope;
+
+  getMerkle(): string;
+  setMerkle(value: string): void;
+
+  serializeBinary(): Uint8Array;
+  toObject(includeInstance?: boolean): SyncResponseAsObject;
+  static toObject(
+    includeInstance: boolean,
+    msg: SyncResponse,
+  ): SyncResponseAsObject;
+  static extensions: { [key: number]: jspb.ExtensionFieldInfo<jspb.Message> };
+  static extensionsBinary: {
+    [key: number]: jspb.ExtensionFieldBinaryInfo<jspb.Message>;
+  };
+  static serializeBinaryToWriter(
+    message: SyncResponse,
+    writer: jspb.BinaryWriter,
+  ): void;
+  static deserializeBinary(bytes: Uint8Array): SyncResponse;
+  static deserializeBinaryFromReader(
+    message: SyncResponse,
+    reader: jspb.BinaryReader,
+  ): SyncResponse;
+}
+
+export type SyncResponseAsObject = {
+  messagesList: Array<MessageEnvelopeAsObject>;
+  merkle: string;
+};
diff --git a/packages/loot-core/src/server/sync/proto/sync_pb.ts b/packages/loot-core/src/server/sync/proto/sync_pb.js
similarity index 100%
rename from packages/loot-core/src/server/sync/proto/sync_pb.ts
rename to packages/loot-core/src/server/sync/proto/sync_pb.js
diff --git a/packages/loot-core/src/server/sync/repair.js b/packages/loot-core/src/server/sync/repair.ts
similarity index 94%
rename from packages/loot-core/src/server/sync/repair.js
rename to packages/loot-core/src/server/sync/repair.ts
index 7de86475eb..96df0b6189 100644
--- a/packages/loot-core/src/server/sync/repair.js
+++ b/packages/loot-core/src/server/sync/repair.ts
@@ -3,7 +3,7 @@ import * as db from '../db';
 
 export function rebuildMerkleHash() {
   let rows = db.runQuery('SELECT timestamp FROM messages_crdt', [], true);
-  let trie = {};
+  let trie: Record<string, unknown> = {};
 
   for (let i = 0; i < rows.length; i++) {
     trie = merkle.insert(trie, Timestamp.parse(rows[i].timestamp));
diff --git a/packages/loot-core/src/server/sync/reset.js b/packages/loot-core/src/server/sync/reset.ts
similarity index 100%
rename from packages/loot-core/src/server/sync/reset.js
rename to packages/loot-core/src/server/sync/reset.ts
diff --git a/packages/loot-core/src/server/sync/sync.property.test.js b/packages/loot-core/src/server/sync/sync.property.test.ts
similarity index 96%
rename from packages/loot-core/src/server/sync/sync.property.test.js
rename to packages/loot-core/src/server/sync/sync.property.test.ts
index 454a1f3d26..0b636cbde8 100644
--- a/packages/loot-core/src/server/sync/sync.property.test.js
+++ b/packages/loot-core/src/server/sync/sync.property.test.ts
@@ -1,4 +1,4 @@
-import jsc from 'jsverify';
+import jsc, { type Arbitrary } from 'jsverify';
 
 import { merkle, getClock, Timestamp } from '../crdt';
 import * as db from '../db';
@@ -10,9 +10,9 @@ import * as encoder from './encoder';
 
 import * as sync from './index';
 
-const uuidGenerator = jsc.integer({ min: 97, max: 122 }).smap(
+const uuidGenerator = jsc.integer(97, 122).smap(
   x => String.fromCharCode(x),
-  x => x.charCodeAt(x),
+  x => x.charCodeAt(Number(x)),
 );
 
 beforeEach(() => {
@@ -98,13 +98,23 @@ let baseTime = 1565374471903;
 let clientId1 = '80dd7da215247293';
 let clientId2 = '90xU1sd5124329ac';
 
-function makeGen({ table, row, field, value }) {
+function makeGen({
+  table,
+  row,
+  field,
+  value,
+}: {
+  table: string;
+  row?: Arbitrary<string>;
+  field: string;
+  value: Arbitrary<unknown>;
+}) {
   return jsc.record({
     dataset: jsc.constant(table),
     row: row || uuidGenerator,
     column: jsc.constant(field),
     value,
-    timestamp: jsc.integer({ min: 1000, max: 10000 }).smap(
+    timestamp: jsc.integer(1000, 10000).smap(
       x => {
         let clientId;
         switch (jsc.random(0, 1)) {
@@ -117,7 +127,7 @@ function makeGen({ table, row, field, value }) {
         }
         return new Timestamp(baseTime + x, 0, clientId);
       },
-      x => x.millis - baseTime,
+      x => x.millis() - baseTime,
     ),
   });
 }
diff --git a/packages/loot-core/src/server/sync/sync.test.js b/packages/loot-core/src/server/sync/sync.test.ts
similarity index 99%
rename from packages/loot-core/src/server/sync/sync.test.js
rename to packages/loot-core/src/server/sync/sync.test.ts
index a1fa6e0601..749891b863 100644
--- a/packages/loot-core/src/server/sync/sync.test.js
+++ b/packages/loot-core/src/server/sync/sync.test.ts
@@ -167,7 +167,7 @@ function expectCellToExist(sheetName, name) {
   expect(value).not.toBe(null);
 }
 
-function expectCellNotToExist(sheetName, name, voided) {
+function expectCellNotToExist(sheetName, name, voided?: boolean) {
   let value = sheet.get().getCellValueLoose(sheetName, name);
   expect(value).toBe(voided ? 0 : null);
 }
diff --git a/packages/loot-core/src/server/tests/mockSyncServer.js b/packages/loot-core/src/server/tests/mockSyncServer.ts
similarity index 98%
rename from packages/loot-core/src/server/tests/mockSyncServer.js
rename to packages/loot-core/src/server/tests/mockSyncServer.ts
index f279b068a7..cb4a3f2639 100644
--- a/packages/loot-core/src/server/tests/mockSyncServer.js
+++ b/packages/loot-core/src/server/tests/mockSyncServer.ts
@@ -1,7 +1,7 @@
 import { makeClock, Timestamp, merkle } from '../crdt';
 import * as SyncPb from '../sync/proto/sync_pb';
 
-import { basic as defaultMockData } from './mockData';
+import { basic as defaultMockData } from './mockData.json';
 
 const handlers = {};
 let currentMockData = defaultMockData;
diff --git a/packages/loot-core/src/server/tools/app.js b/packages/loot-core/src/server/tools/app.ts
similarity index 100%
rename from packages/loot-core/src/server/tools/app.js
rename to packages/loot-core/src/server/tools/app.ts
diff --git a/packages/loot-core/src/server/util/budget-name.js b/packages/loot-core/src/server/util/budget-name.ts
similarity index 100%
rename from packages/loot-core/src/server/util/budget-name.js
rename to packages/loot-core/src/server/util/budget-name.ts
diff --git a/packages/loot-core/src/server/util/rschedule.js b/packages/loot-core/src/server/util/rschedule.ts
similarity index 100%
rename from packages/loot-core/src/server/util/rschedule.js
rename to packages/loot-core/src/server/util/rschedule.ts
diff --git a/packages/loot-core/src/shared/accounts.ts b/packages/loot-core/src/shared/accounts.ts
index 223a79a2bb..668ca00c17 100644
--- a/packages/loot-core/src/shared/accounts.ts
+++ b/packages/loot-core/src/shared/accounts.ts
@@ -1,4 +1,4 @@
-export function fromPlaidAccountType(type, subtype) {
+export function fromPlaidAccountType(type, subtype?: string) {
   switch (type) {
     case 'brokerage':
     case 'investment':
diff --git a/packages/loot-core/src/shared/async.ts b/packages/loot-core/src/shared/async.ts
index eb85c23449..3739a4e3d5 100644
--- a/packages/loot-core/src/shared/async.ts
+++ b/packages/loot-core/src/shared/async.ts
@@ -1,4 +1,6 @@
-export function sequential(fn) {
+export function sequential<T extends (...args: unknown[]) => unknown>(
+  fn: T,
+): (...args: Parameters<T>) => Promise<ReturnType<T>> {
   let sequenceState = {
     running: null,
     queue: [],
diff --git a/packages/loot-core/src/shared/rules.ts b/packages/loot-core/src/shared/rules.ts
index b4295c6faa..3a58c973f7 100644
--- a/packages/loot-core/src/shared/rules.ts
+++ b/packages/loot-core/src/shared/rules.ts
@@ -25,6 +25,19 @@ export const TYPE_INFO = {
   },
 };
 
+export type FieldTypes = {
+  imported_payee: string;
+  payee: string;
+  date: string;
+  notes: string;
+  amount: number;
+  amountInflow: number;
+  amountOutfow: number;
+  category: string;
+  account: string;
+  cleared: boolean;
+};
+
 export const FIELD_TYPES = new Map(
   Object.entries({
     imported_payee: 'string',
diff --git a/packages/loot-core/src/shared/schedules.ts b/packages/loot-core/src/shared/schedules.ts
index 0181e6ecd6..3844c098a5 100644
--- a/packages/loot-core/src/shared/schedules.ts
+++ b/packages/loot-core/src/shared/schedules.ts
@@ -1,3 +1,5 @@
+import type { IRuleOptions } from '@rschedule/core';
+
 import * as monthUtils from './months';
 import q from './query';
 
@@ -156,15 +158,8 @@ export function getRecurringDescription(config) {
   }
 }
 
-type RecurringSchedule = {
-  start: Date;
-  frequency: string;
-  byHourOfDay: number[];
-  interval?: unknown;
-};
-
 export function recurConfigToRSchedule(config) {
-  let base: RecurringSchedule = {
+  let base: IRuleOptions = {
     start: monthUtils.parseDate(config.start),
     frequency: config.frequency.toUpperCase(),
     byHourOfDay: [12],
diff --git a/packages/loot-core/src/shared/test-helpers.ts b/packages/loot-core/src/shared/test-helpers.ts
index 36e2ade775..6c3d499f75 100644
--- a/packages/loot-core/src/shared/test-helpers.ts
+++ b/packages/loot-core/src/shared/test-helpers.ts
@@ -27,7 +27,7 @@ export function execTracer() {
   let log = false;
 
   return {
-    event(name, data) {
+    event(name: string, data?: unknown) {
       if (!hasStarted) {
         return;
       } else if (log) {
@@ -122,7 +122,7 @@ export function execTracer() {
       }
     },
 
-    expect(name, data) {
+    expect(name: string, data?: unknown) {
       if (queue.length === 0) {
         return this.expectWait(name, data);
       }
diff --git a/packages/loot-core/src/shared/util.ts b/packages/loot-core/src/shared/util.ts
index b62bf249d7..1cc1cb9321 100644
--- a/packages/loot-core/src/shared/util.ts
+++ b/packages/loot-core/src/shared/util.ts
@@ -121,7 +121,7 @@ export function partitionByField(data, field) {
   return res;
 }
 
-export function groupBy(data, field, mapper) {
+export function groupBy(data, field, mapper?: (v: unknown) => unknown) {
   let res = new Map();
   for (let i = 0; i < data.length; i++) {
     let item = data[i];
diff --git a/packages/loot-core/src/types/api.handlers.d.ts b/packages/loot-core/src/types/api.handlers.d.ts
new file mode 100644
index 0000000000..962f081d71
--- /dev/null
+++ b/packages/loot-core/src/types/api.handlers.d.ts
@@ -0,0 +1,123 @@
+export interface ApiHandlers {
+  'api/batch-budget-start': () => Promise<unknown>;
+
+  'api/batch-budget-end': () => Promise<unknown>;
+
+  'api/load-budget': (
+    ...args: Parameters<ServerHandlers['load-budget']>
+  ) => Promise<unknown>;
+
+  'api/download-budget': (arg: { syncId; password }) => Promise<unknown>;
+
+  'api/start-import': (arg: { budgetName }) => Promise<unknown>;
+
+  'api/finish-import': () => Promise<unknown>;
+
+  'api/abort-import': () => Promise<unknown>;
+
+  'api/query': (arg: { query }) => Promise<unknown>;
+
+  'api/budget-months': () => Promise<unknown>;
+
+  'api/budget-month': (arg: { month }) => Promise<{
+    month;
+    incomeAvailable: number;
+    lastMonthOverspent: number;
+    forNextMonth: number;
+    totalBudgeted: number;
+    toBudget: number;
+
+    fromLastMonth: number;
+    totalIncome: number;
+    totalSpent: number;
+    totalBalance: number;
+    categoryGroups: Record<string, unknown>[];
+  }>;
+
+  'api/budget-set-amount': (arg: {
+    month;
+    categoryId;
+    amount;
+  }) => Promise<unknown>;
+
+  'api/budget-set-carryover': (arg: {
+    month;
+    categoryId;
+    flag;
+  }) => Promise<unknown>;
+
+  'api/transactions-export': (arg: {
+    transactions;
+    categoryGroups;
+    payees;
+  }) => Promise<unknown>;
+
+  'api/transactions-import': (arg: {
+    accountId;
+    transactions;
+  }) => Promise<unknown>;
+
+  'api/transactions-add': (arg: { accountId; transactions }) => Promise<'ok'>;
+
+  'api/transactions-get': (arg: {
+    accountId;
+    startDate;
+    endDate;
+  }) => Promise<unknown>;
+
+  /** @deprecated `filterTransactions` is deprecated, use `runQuery` instead' */
+  'api/transactions-filter': (arg: { text; accountId }) => Promise<void>;
+
+  'api/transaction-update': (arg: { id; fields }) => Promise<unknown>;
+
+  'api/transaction-delete': (arg: { id }) => Promise<unknown>;
+
+  'api/accounts-get': () => Promise<unknown>;
+
+  'api/account-create': (arg: { account; initialBalance }) => Promise<unknown>;
+
+  'api/account-update': (arg: { id; fields }) => Promise<unknown>;
+
+  'api/account-close': (arg: {
+    id;
+    transferAccountId;
+    transferCategoryId;
+  }) => Promise<unknown>;
+
+  'api/account-reopen': (arg: { id }) => Promise<unknown>;
+
+  'api/account-delete': (arg: { id }) => Promise<unknown>;
+
+  'api/categories-get': (arg: { grouped }) => Promise<unknown>;
+
+  'api/category-group-create': (arg: { group }) => Promise<unknown>;
+
+  'api/category-group-update': (arg: { id; fields }) => Promise<unknown>;
+
+  'api/category-group-delete': (arg: {
+    id;
+    transferCategoryId;
+  }) => Promise<unknown>;
+
+  'api/category-create': (arg: { category }) => Promise<unknown>;
+
+  'api/category-update': (arg: { id; fields }) => Promise<unknown>;
+
+  'api/category-delete': (arg: { id; transferCategoryId }) => Promise<unknown>;
+
+  'api/payees-get': () => Promise<unknown>;
+
+  'api/payee-create': (arg: { payee }) => Promise<unknown>;
+
+  'api/payee-update': (arg: { id; fields }) => Promise<unknown>;
+
+  'api/payee-delete': (arg: { id }) => Promise<unknown>;
+
+  'api/payee-rules-get': (arg: { payeeId }) => Promise<unknown>;
+
+  'api/payee-rule-create': (arg: { payee_id; rule }) => Promise<unknown>;
+
+  'api/payee-rule-update': (arg: { id; fields }) => Promise<unknown>;
+
+  'api/payee-rule-delete': (arg: { id }) => Promise<unknown>;
+}
diff --git a/packages/loot-core/src/types/handlers.d.ts b/packages/loot-core/src/types/handlers.d.ts
new file mode 100644
index 0000000000..e4eb27a098
--- /dev/null
+++ b/packages/loot-core/src/types/handlers.d.ts
@@ -0,0 +1,12 @@
+import type { BudgetHandlers } from '../server/budget/types/handlers';
+import type { NotesHandlers } from '../server/notes/types/handlers';
+import type { SchedulesHandlers } from '../server/schedules/types/handlers';
+
+import type { ApiHandlers } from './api.handlers';
+import type { MainHandlers } from './main.handlers';
+
+export type Handlers = MainHandlers &
+  ApiHandlers &
+  BudgetHandlers &
+  NotesHandlers &
+  SchedulesHandlers;
diff --git a/packages/loot-core/src/types/main.handlers.d.ts b/packages/loot-core/src/types/main.handlers.d.ts
new file mode 100644
index 0000000000..51d1065faa
--- /dev/null
+++ b/packages/loot-core/src/types/main.handlers.d.ts
@@ -0,0 +1,340 @@
+export interface MainHandlers {
+  'transaction-update': (
+    transaction: unknown,
+  ) => Promise<Record<string, never>>;
+
+  undo: () => Promise<unknown>;
+
+  redo: () => Promise<unknown>;
+
+  'transactions-batch-update': (arg: {
+    added;
+    deleted;
+    updated;
+    learnCategories;
+  }) => Promise<unknown>;
+
+  'transaction-add': (transaction) => Promise<Record<string, never>>;
+
+  'transaction-aupdatedd': (transaction) => Promise<Record<string, never>>;
+
+  'transaction-delete': (transaction) => Promise<Record<string, never>>;
+
+  'transactions-filter': (arg: {
+    term;
+    accountId;
+    latestDate;
+    count;
+    notPaged;
+    options;
+  }) => Promise<unknown>;
+
+  'transactions-parse-file': (arg: { filepath; options }) => Promise<unknown>;
+
+  'transactions-export': (arg: {
+    transactions;
+    accounts;
+    categoryGroups;
+    payees;
+  }) => Promise<unknown>;
+
+  'transactions-export-query': (arg: { query: queryState }) => Promise<unknown>;
+
+  'get-categories': () => Promise<{
+    grouped: unknown;
+    list: unknown;
+  }>;
+
+  'get-earliest-transaction': () => Promise<unknown>;
+
+  'get-budget-bounds': () => Promise<unknown>;
+
+  'rollover-budget-month': (arg: { month }) => Promise<unknown>;
+
+  'report-budget-month': (arg: { month }) => Promise<unknown>;
+
+  'budget-set-type': (arg: { type }) => Promise<unknown>;
+
+  'category-create': (arg: { name; groupId; isIncome }) => Promise<unknown>;
+
+  'category-update': (category) => Promise<unknown>;
+
+  'category-move': (arg: { id; groupId; targetId }) => Promise<unknown>;
+
+  'category-delete': (arg: { id; transferId }) => Promise<{ error }>;
+
+  'category-group-create': (arg: {
+    name;
+    isIncome?: boolean;
+  }) => Promise<unknown>;
+
+  'category-group-update': (group) => Promise<unknown>;
+
+  'category-group-move': (arg: { id; targetId }) => Promise<unknown>;
+
+  'category-group-delete': (arg: { id; transferId }) => Promise<unknown>;
+
+  'must-category-transfer': (arg: { id }) => Promise<unknown>;
+
+  'payee-create': (arg: { name }) => Promise<unknown>;
+
+  'payees-get': () => Promise<unknown>;
+
+  'payees-get-rule-counts': () => Promise<unknown>;
+
+  'payees-merge': (arg: { targetId; mergeIds }) => Promise<unknown>;
+
+  'payees-batch-change': (arg: { added; deleted; updated }) => Promise<unknown>;
+
+  'payees-check-orphaned': (arg: { ids }) => Promise<unknown>;
+
+  'payees-get-rules': (arg: { id }) => Promise<unknown>;
+
+  'payees-delete-rule': (arg: { id; payee_id }) => Promise<unknown>;
+
+  'payees-update-rule': (rule) => Promise<unknown>;
+
+  'payees-add-rule': (rule) => Promise<unknown>;
+
+  'rule-validate': (rule) => Promise<{ error: unknown }>;
+
+  'rule-add': (rule) => Promise<{ error: unknown } | { id: string }>;
+
+  'rule-add': (rule) => Promise<{ error: unknown } | unknown>;
+
+  'rule-delete': (rule) => Promise<unknown>;
+
+  'rule-delete-all': (ids) => Promise<unknown>;
+
+  'rule-apply-actions': (arg: { transactionIds; actions }) => Promise<unknown>;
+
+  'rule-add-payee-rename': (arg: { fromNames; to }) => Promise<unknown>;
+
+  'rules-get': () => Promise<unknown>;
+
+  'rule-get': (arg: { id }) => Promise<unknown>;
+
+  'rules-run': (arg: { transaction }) => Promise<unknown>;
+
+  'rules-migrate': () => Promise<unknown>;
+
+  'make-filters-from-conditions': (arg: { conditions }) => Promise<unknown>;
+
+  getCell: (arg: { sheetName; name }) => Promise<unknown>;
+
+  getCells: (arg: { names }) => Promise<unknown>;
+
+  getCellNamesInSheet: (arg: { sheetName }) => Promise<unknown>;
+
+  debugCell: (arg: { sheetName; name }) => Promise<unknown>;
+
+  'create-query': (arg: { sheetName; name; query }) => Promise<unknown>;
+
+  query: (query) => Promise<unknown>;
+
+  'bank-delete': (arg: { id }) => Promise<unknown>;
+
+  'account-update': (arg: { id; name }) => Promise<unknown>;
+
+  'accounts-get': () => Promise<unknown>;
+
+  'account-properties': (arg: {
+    id;
+  }) => Promise<{ balance: number; numTransactions: number }>;
+
+  'accounts-link': (arg: {
+    institution;
+    publicToken;
+    accountId;
+    upgradingId;
+  }) => Promise<'ok'>;
+
+  'nordigen-accounts-link': (arg: {
+    requisitionId;
+    account;
+    upgradingId;
+  }) => Promise<'ok'>;
+
+  'accounts-connect': (arg: {
+    institution;
+    publicToken;
+    accountIds;
+    offbudgetIds;
+  }) => Promise<unknown>;
+
+  'nordigen-accounts-connect': (arg: {
+    institution;
+    publicToken;
+    accountIds;
+    offbudgetIds;
+  }) => Promise<unknown>;
+
+  'account-create': (arg: {
+    name;
+    type;
+    balance;
+    offBudget;
+    closed?;
+  }) => Promise<string>;
+
+  'account-close': (arg: {
+    id;
+    transferAccountId;
+    categoryId;
+    forced;
+  }) => Promise<unknown>;
+
+  'account-reopen': (arg: { id }) => Promise<unknown>;
+
+  'account-move': (arg: { id; targetId }) => Promise<unknown>;
+
+  'poll-web-token': (arg: { token }) => Promise<unknown>;
+
+  'poll-web-token-stop': () => Promise<'ok'>;
+
+  'accounts-sync': (arg: { id }) => Promise<{
+    errors: unknown;
+    newTransactions: unknown;
+    matchedTransactions: unknown;
+    updatedAccounts: unknown;
+  }>;
+
+  'nordigen-poll-web-token': (arg: {
+    upgradingAccountId;
+    requisitionId;
+  }) => Promise<null>;
+
+  'nordigen-status': () => Promise<unknown>;
+
+  'nordigen-get-banks': (country) => Promise<unknown>;
+
+  'nordigen-poll-web-token-stop': () => Promise<'ok'>;
+
+  'nordigen-create-web-token': (arg: {
+    upgradingAccountId;
+    institutionId;
+    accessValidForDays;
+  }) => Promise<unknown>;
+
+  'nordigen-accounts-sync': (arg: { id }) => Promise<{
+    errors;
+    newTransactions;
+    matchedTransactions;
+    updatedAccounts;
+  }>;
+
+  'transactions-import': (arg: { accountId; transactions }) => Promise<{
+    errors;
+    added;
+    updated;
+  }>;
+
+  'account-unlink': (arg: { id }) => Promise<'ok'>;
+
+  'make-plaid-public-token': (arg: {
+    bankId;
+  }) => Promise<
+    | { error: ''; code: data.error_code; type: data.error_type }
+    | { linkToken: data.link_token }
+  >;
+
+  'save-global-prefs': (prefs) => Promise<'ok'>;
+
+  'load-global-prefs': () => Promise<{
+    floatingSidebar: boolean;
+    seenTutorial: boolean;
+    maxMonths: number;
+    autoUpdate: boolean;
+    documentDir: string;
+    keyId: string;
+  }>;
+
+  'save-prefs': (prefsToSet) => Promise<'ok'>;
+
+  'load-prefs': () => Promise<Record<string, unknown> | null>;
+
+  'sync-reset': () => Promise<{ error }>;
+
+  'sync-repair': () => Promise<unknown>;
+
+  'key-make': (arg: { password }) => Promise<unknown>;
+
+  'key-test': (arg: { fileId; password }) => Promise<unknown>;
+
+  'subscribe-needs-bootstrap': (
+    args: { url } = {},
+  ) => Promise<
+    { error: string } | { bootstrapped: unknown; hasServer: boolean }
+  >;
+
+  'subscribe-bootstrap': (arg: { password }) => Promise<{ error: string }>;
+
+  'subscribe-set-user': (arg: { token }) => Promise<unknown>;
+
+  'subscribe-get-user': () => Promise<{ offline: boolean } | null>;
+
+  'subscribe-change-password': (arg: {
+    password;
+  }) => Promise<{ error: string }>;
+
+  'subscribe-sign-in': (arg: { password }) => Promise<{ error: string }>;
+
+  'subscribe-sign-out': () => Promise<'ok'>;
+
+  'get-server-version': () => Promise<{ error: string } | { version: string }>;
+
+  'get-server-url': () => Promise<unknown>;
+
+  'set-server-url': (arg: { url; validate }) => Promise<unknown>;
+
+  sync: () => Promise<{ error: string }>;
+
+  'get-budgets': () => Promise<unknown>;
+
+  'get-remote-files': () => Promise<unknown>;
+
+  'reset-budget-cache': () => Promise<unknown>;
+
+  'upload-budget': (arg: { id } = {}) => Promise<{ error }>;
+
+  'download-budget': (arg: { fileId; replace }) => Promise<{ error; id }>;
+
+  'sync-budget': (arg: { id }) => Promise<unknown>;
+
+  'load-budget': (arg: { id }) => Promise<{ error }>;
+
+  'create-demo-budget': () => Promise<unknown>;
+
+  'close-budget': () => Promise<'ok'>;
+
+  'delete-budget': (arg: { id; cloudFileId }) => Promise<'ok'>;
+
+  'create-budget': (arg: {
+    budgetName?;
+    avoidUpload?;
+    testMode: boolean;
+    testBudgetId?;
+  }) => Promise<unknown>;
+
+  'set-tutorial-seen': () => Promise<'ok'>;
+
+  'import-budget': (arg: { filepath; type }) => Promise<{ error }>;
+
+  'export-budget': () => Promise<unknown>;
+
+  'get-upgrade-notifications': () => Promise<unknown[]>;
+
+  'seen-upgrade-notification': (arg: { type }) => Promise<unknown>;
+
+  'upload-file-web': (arg: { filename; contents }) => Promise<'ok'>;
+
+  'backups-get': (arg: { id }) => Promise<unknown>;
+
+  'backup-load': (arg: { id; backupId }) => Promise<unknown>;
+
+  'backup-make': (arg: { id }) => Promise<unknown>;
+
+  'get-last-opened-backup': () => Promise<unknown>;
+
+  'app-focused': () => Promise<unknown>;
+}
diff --git a/packages/loot-core/typings.d.ts b/packages/loot-core/typings.d.ts
new file mode 100644
index 0000000000..40fd9d9516
--- /dev/null
+++ b/packages/loot-core/typings.d.ts
@@ -0,0 +1 @@
+declare module '*.pegjs';
diff --git a/upcoming-release-notes/896.md b/upcoming-release-notes/896.md
new file mode 100644
index 0000000000..af1da3d8a6
--- /dev/null
+++ b/upcoming-release-notes/896.md
@@ -0,0 +1,6 @@
+---
+category: Maintenance
+authors: [albertogasparin]
+---
+
+Convert few more folders in `loot-core` to Typescript
diff --git a/yarn.lock b/yarn.lock
index 0815186f7a..f352d13e28 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3577,6 +3577,15 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@types/better-sqlite3@npm:^7.6.4":
+  version: 7.6.4
+  resolution: "@types/better-sqlite3@npm:7.6.4"
+  dependencies:
+    "@types/node": "*"
+  checksum: 75ab00d31b56437cc65fe15ff673cf8d1609edca52628083921bcbab1cbd828d135a2859fb4e68af8ef5a4801705ba99d54b96499f997bce65dd306ade3dbe58
+  languageName: node
+  linkType: hard
+
 "@types/body-parser@npm:*":
   version: 1.19.2
   resolution: "@types/body-parser@npm:1.19.2"
@@ -3956,6 +3965,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@types/pegjs@npm:^0.10.3":
+  version: 0.10.3
+  resolution: "@types/pegjs@npm:0.10.3"
+  checksum: b0301595d7d7da4de9f8edcc8a97ee55c959e74645dd49626bbaf344dd383e1491b43082d34c1f55048566fef21bf219a4b4743f770afbe80a390a3a33926b8a
+  languageName: node
+  linkType: hard
+
 "@types/plist@npm:^3.0.1":
   version: 3.0.2
   resolution: "@types/plist@npm:3.0.2"
@@ -10489,6 +10505,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"google-protobuf@npm:^3.15.5":
+  version: 3.21.2
+  resolution: "google-protobuf@npm:3.21.2"
+  checksum: 3caa2e1e2654714cc1a201ac5e5faabcaa48f5fba3d8ff9b64ca66fe19e4e0506b94053f32eddc77bf3a7a47ac1660315c6744185c1e2bb27654fd76fe91b988
+  languageName: node
+  linkType: hard
+
 "gopd@npm:^1.0.1":
   version: 1.0.1
   resolution: "gopd@npm:1.0.1"
@@ -13406,9 +13429,11 @@ __metadata:
     "@rschedule/ical-tools": ^1.2.0
     "@rschedule/json-tools": ^1.2.0
     "@rschedule/standard-date-adapter": ^1.2.0
+    "@types/better-sqlite3": ^7.6.4
     "@types/jest": ^27.5.0
     "@types/jlongster__sql.js": "npm:@types/sql.js@latest"
     "@types/node-ipc": ^9.2.0
+    "@types/pegjs": ^0.10.3
     "@types/webpack": ^5.28.0
     "@wademason/ofx": 1.0.1
     absurd-sql: 0.0.53
@@ -13443,6 +13468,7 @@ __metadata:
     throttleit: ^1.0.0
     ts-jest: ^27.0.0
     ts-node: ^10.7.0
+    ts-protoc-gen: ^0.15.0
     typescript: ^4.6.4
     uuid: 3.3.2
     webpack: ^4.41.2
@@ -19562,6 +19588,17 @@ __metadata:
   languageName: node
   linkType: hard
 
+"ts-protoc-gen@npm:^0.15.0":
+  version: 0.15.0
+  resolution: "ts-protoc-gen@npm:0.15.0"
+  dependencies:
+    google-protobuf: ^3.15.5
+  bin:
+    protoc-gen-ts: bin/protoc-gen-ts
+  checksum: 612799180832786ee28dfb3510015f840ff8acd480ec1159599535878cc77a4f6ad4d6993d1fa546bbb4523de5fb60f4987e1ea810c2e56d91be0448d30f29ad
+  languageName: node
+  linkType: hard
+
 "tsconfig-paths@npm:^3.14.1":
   version: 3.14.1
   resolution: "tsconfig-paths@npm:3.14.1"