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[GH-ISSUE #20629] issue: MCP server response fails #34768
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Originally created by @thrasher on GitHub (Jan 12, 2026).
Original GitHub issue: https://github.com/open-webui/open-webui/issues/20629
Check Existing Issues
Installation Method
Docker
Open WebUI Version
v0.7.2
Ollama Version (if applicable)
v0.13.5
Operating System
MacOS Tahoe 26.1
Browser (if applicable)
Chrome 143.0.7499.193
Confirmation
README.md.Expected Behavior
After adding a local MCP server, a chat submitted through Open-WebUI should use data from the MCP server to render a response using ollama.
Actual Behavior
An error is generated where the chat response should be:

cannot pickle '_asyncio.Future' object
Steps to Reproduce
Start running a fresh docker image
Run a local MCP server, using FastMCP v2.14.2 (latest):
Code for mcp_server.py
Configure Open-WebUI to use the MCP Server.
Navigate: Admin Panel / Settings / External Tools / "+"
Set as follows:
Test the connection:
In Open-WebUI, enable the MCP tool:
Submit a new chat "What is the weather in Berlin?"
Observe the error message:
Observe the console output for the FastMCP server.
Logs & Screenshots
The Chrome dev tools console has one warning, but no errors:
RichTextInput.svelte:690 [tiptap warn]: Duplicate extension names found: ['codeBlock', 'bulletList', 'listItem', 'listKeymap', 'orderedList']. This can lead to issues.
Additional Information
The pickle error seems informative in that some data is not getting (de) serialized properly. I grepped through the codebase but wasn't sure where this might be.
This MCP server works as expected when registered in Visual Studio Code, and then asked for the weather in Berlin with the same query (as well as the other @mcp.tools).
@owui-terminator[bot] commented on GitHub (Jan 12, 2026):
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@Jannled commented on GitHub (Jan 12, 2026):
I was about to report the same issue.
f2a360c(v0.7.1) worked fine, this issue exists only since v0.7.2.This is the relevant server log entry:
To anyone looking into the problem: Since things are passed to pickle that should not end up there, please also make sure that no unvalidated user input is able to escape into pickle, as this could become a security vulnerability.
@mighty-drive commented on GitHub (Jan 13, 2026):
Yep, confirming that it worked in previous versions.
@raufis27 commented on GitHub (Jan 13, 2026):
Getting the same error after upgrading to the latest v0.7.2
@jurschel-gmt commented on GitHub (Jan 13, 2026):
Yes reverted back to v0.7.1 and the problem goes away.
@alexbenedek commented on GitHub (Jan 14, 2026):
Damn !!! i was getting insane over this for 3 days .... downgraded to 0.7.1 and it works ...ughhhh
Thanks!
@see-gee commented on GitHub (Jan 16, 2026):
I am also having this exact same problem... Spent some time on this before I found this post.
@dota-devy commented on GitHub (Jan 17, 2026):
I am also seeing this behavior on v0.7.2
@meremortals70 commented on GitHub (Jan 17, 2026):
same issue here
@a-phasia commented on GitHub (Jan 18, 2026):
same issue, reverting to 0.7.1 fixed the issue for me too.
@thrasher commented on GitHub (Jan 19, 2026):
I've also verified that 0.7.1 fixes the issue. Thanks to @KoulLife for the patch!
@null-create commented on GitHub (Jan 19, 2026):
Confirming that the issue appears to be happening with v0.7.2, and that reverting to 0.7.1 resolves the issue
@tjbck commented on GitHub (Jan 22, 2026):
Could anyone confirm that the issue has been resolved in our dev branch? 0.7.3 should be released shortly
@jurschel-gmt commented on GitHub (Jan 22, 2026):
@tjbck ,
I can confirm to you that the problem is resolved. Even though the code still says it's 0.7.2 the direct_url.json tells me I'm on the dev branch commit. I successfully made a call out to my mcp-sql tool and got a response with no pickle error.
Version: 0.7.2
Direct URL: {"url": "https://github.com/open-webui/open-webui.git", "vcs_info": {"commit_id": "9af40624c5f0f8f7f640a11356e167543b07b2bb", "requested_revision": "dev", "vcs": "git"}}
@Slyefox commented on GitHub (Jan 24, 2026):
Confirmed: v0.6.43 works perfectly, v0.7.2 breaks MCP with pickle error
@taylorwilsdon commented on GitHub (Jan 29, 2026):
@tjbck it is fixed in dev btw looking forward to the release
@Classic298 commented on GitHub (Jan 29, 2026):
@taylorwilsdon is that a question or a confirmation? (fmi)
@Classic298 commented on GitHub (Jan 29, 2026):
great!
@meremortals70 commented on GitHub (Jan 30, 2026):
look forward to the release
@hasmcp-dev commented on GitHub (Feb 9, 2026):
+1 on this issue. Looking forward to seeing the fix coming in v0.7.3
@mamoit commented on GitHub (Feb 13, 2026):
v0.8.0just dropped, tested the new docker image and the problem is fixed.@neumeierAG commented on GitHub (Feb 26, 2026):
I still geht this error:
@thrasher commented on GitHub (Mar 3, 2026):
@neumeierAG this bug is closed and confirmed resolved. The error you posted doesn't show how it is related to this bug. I recommend either filing a new bug or searching for a better match to an existing one that is open.