This is a fix IF the fix for this issue even belongs in Open WebUI. I'm not sure of the actual best place this one should be fixed, so have raised a discussion for this issue here - https://github.com/open-webui/open-webui/discussions/14882. Discussion has diagrams and more details.
I feel like the fix for this issue does belong in Open WebUI, but feel free to just close this PR if you think it actually belongs somewhere else (e.g. bedrock gateway). If it does belong here, but the late mutation is a bit ugly, I can move it up closer to the response stream receiving part.
Pull Request Checklist
Before submitting, make sure you've checked the following:
Target branch: Please verify that the pull request targets the dev branch.
Description: Provide a concise description of the changes made in this pull request.
Changelog: Ensure a changelog entry following the format of Keep a Changelog is added at the bottom of the PR description.
Documentation: Have you updated relevant documentation Open WebUI Docs, or other documentation sources?
Dependencies: Are there any new dependencies? Have you updated the dependency versions in the documentation?
Testing: Have you written and run sufficient tests to validate the changes?
Code review: Have you performed a self-review of your code, addressing any coding standard issues and ensuring adherence to the project's coding standards?
Prefix: fix: MCP Tools with Empty Arguments JSON Parsing Error
Changelog Entry
Description
Fixed JSON parsing errors when MCP (Model Context Protocol) tools with no arguments are executed, preventing "Expecting value: line 1 column 1 (char 0)" errors
Added NODE_OPTIONS build argument support to prevent frontend build memory allocation failures during Docker builds
Changed
Tool call argument processing in middleware to convert empty argument strings to valid JSON objects before tool execution
Debug log to an actual error log.
Fixed
MCP Tool Execution: Fixed JSON parsing errors when MCP tools with no arguments are called, where empty argument strings "" are now properly converted to valid JSON empty objects "{}"
Security
[None]
Breaking Changes
[None - changes are backward compatible]
Screenshots or Videos
Screenshot shows a before after in a single chat of the error and then fixed
Contributor License Agreement
By submitting this pull request, I confirm that I have read and fully agree to the Contributor License Agreement (CLA), and I am providing my contributions under its terms.
🔄 This issue represents a GitHub Pull Request. It cannot be merged through Gitea due to API limitations.
## 📋 Pull Request Information
**Original PR:** https://github.com/open-webui/open-webui/pull/14886
**Author:** [@2underscores](https://github.com/2underscores)
**Created:** 6/11/2025
**Status:** ✅ Merged
**Merged:** 6/16/2025
**Merged by:** [@tjbck](https://github.com/tjbck)
**Base:** `dev` ← **Head:** `fix-no-arg-mcp-call`
---
### 📝 Commits (1)
- [`88c8ea8`](https://github.com/open-webui/open-webui/commit/88c8ea883cd2142b70925a08790ea089946d37e0) Isolated fix to single section
### 📊 Changes
**1 file changed** (+14 additions, -4 deletions)
<details>
<summary>View changed files</summary>
📝 `backend/open_webui/utils/middleware.py` (+14 -4)
</details>
### 📄 Description
This is a fix IF the fix for this issue even belongs in Open WebUI. I'm not sure of the actual best place this one should be fixed, so have raised a discussion for this issue here - https://github.com/open-webui/open-webui/discussions/14882. Discussion has diagrams and more details.
I feel like the fix for this issue does belong in Open WebUI, but feel free to just close this PR if you think it actually belongs somewhere else (e.g. bedrock gateway). If it does belong here, but the late mutation is a bit ugly, I can move it up closer to the response stream receiving part.
# Pull Request Checklist
**Before submitting, make sure you've checked the following:**
- [x] **Target branch:** Please verify that the pull request targets the `dev` branch.
- [x] **Description:** Provide a concise description of the changes made in this pull request.
- [x] **Changelog:** Ensure a changelog entry following the format of [Keep a Changelog](https://keepachangelog.com/) is added at the bottom of the PR description.
- [ ] **Documentation:** Have you updated relevant documentation [Open WebUI Docs](https://github.com/open-webui/docs), or other documentation sources?
- [ ] **Dependencies:** Are there any new dependencies? Have you updated the dependency versions in the documentation?
- [ ] **Testing:** Have you written and run sufficient tests to validate the changes?
- [x] **Code review:** Have you performed a self-review of your code, addressing any coding standard issues and ensuring adherence to the project's coding standards?
- [x] **Prefix:** fix: MCP Tools with Empty Arguments JSON Parsing Error
# Changelog Entry
### Description
- Fixed JSON parsing errors when MCP (Model Context Protocol) tools with no arguments are executed, preventing "Expecting value: line 1 column 1 (char 0)" errors
- Added NODE_OPTIONS build argument support to prevent frontend build memory allocation failures during Docker builds
### Changed
- Tool call argument processing in middleware to convert empty argument strings to valid JSON objects before tool execution
- Debug log to an actual error log.
### Fixed
- **MCP Tool Execution**: Fixed JSON parsing errors when MCP tools with no arguments are called, where empty argument strings `""` are now properly converted to valid JSON empty objects `"{}"`
### Security
- [None]
### Breaking Changes
- [None - changes are backward compatible]
### Screenshots or Videos
Screenshot shows a before after in a single chat of the error and then fixed
### Contributor License Agreement
By submitting this pull request, I confirm that I have read and fully agree to the [Contributor License Agreement (CLA)](/CONTRIBUTOR_LICENSE_AGREEMENT), and I am providing my contributions under its terms.
---
<sub>🔄 This issue represents a GitHub Pull Request. It cannot be merged through Gitea due to API limitations.</sub>
Blocking a user prevents them from interacting with repositories, such as opening or commenting on pull requests or issues. Learn more about blocking a user.
📋 Pull Request Information
Original PR: https://github.com/open-webui/open-webui/pull/14886
Author: @2underscores
Created: 6/11/2025
Status: ✅ Merged
Merged: 6/16/2025
Merged by: @tjbck
Base:
dev← Head:fix-no-arg-mcp-call📝 Commits (1)
88c8ea8Isolated fix to single section📊 Changes
1 file changed (+14 additions, -4 deletions)
View changed files
📝
backend/open_webui/utils/middleware.py(+14 -4)📄 Description
This is a fix IF the fix for this issue even belongs in Open WebUI. I'm not sure of the actual best place this one should be fixed, so have raised a discussion for this issue here - https://github.com/open-webui/open-webui/discussions/14882. Discussion has diagrams and more details.
I feel like the fix for this issue does belong in Open WebUI, but feel free to just close this PR if you think it actually belongs somewhere else (e.g. bedrock gateway). If it does belong here, but the late mutation is a bit ugly, I can move it up closer to the response stream receiving part.
Pull Request Checklist
Before submitting, make sure you've checked the following:
devbranch.Changelog Entry
Description
Changed
Fixed
""are now properly converted to valid JSON empty objects"{}"Security
Breaking Changes
Screenshots or Videos
Screenshot shows a before after in a single chat of the error and then fixed
Contributor License Agreement
By submitting this pull request, I confirm that I have read and fully agree to the Contributor License Agreement (CLA), and I am providing my contributions under its terms.
🔄 This issue represents a GitHub Pull Request. It cannot be merged through Gitea due to API limitations.