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[GH-ISSUE #19486] issue: MCP tool loading fails with "'list' object has no attribute 'split'" when function_name_filter_list is empty #34427

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opened 2026-04-25 08:25:04 -05:00 by GiteaMirror · 12 comments
GiteaMirror commented 2026-04-25 08:25:04 -05:00
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Originally created by @kathrynalpert on GitHub (Nov 25, 2025).
Original GitHub issue: https://github.com/open-webui/open-webui/issues/19486

Check Existing Issues

  • I have searched for any existing and/or related issues.
  • I have searched for any existing and/or related discussions.
  • I have also searched in the CLOSED issues AND CLOSED discussions and found no related items (your issue might already be addressed on the development branch!).
  • I am using the latest version of Open WebUI.

Installation Method

Docker

Open WebUI Version

v0.6.40

Ollama Version (if applicable)

No response

Operating System

Debian Bookworm (Docker: python:3.11-slim-bookworm)

Browser (if applicable)

No response

Confirmation

  • I have read and followed all instructions in README.md.
  • I am using the latest version of both Open WebUI and Ollama.
  • I have included the browser console logs.
  • I have included the Docker container logs.
  • I have provided every relevant configuration, setting, and environment variable used in my setup.
  • I have clearly listed every relevant configuration, custom setting, environment variable, and command-line option that influences my setup (such as Docker Compose overrides, .env values, browser settings, authentication configurations, etc).
  • I have documented step-by-step reproduction instructions that are precise, sequential, and leave nothing to interpretation. My steps:
  • Start with the initial platform/version/OS and dependencies used,
  • Specify exact install/launch/configure commands,
  • List URLs visited, user input (incl. example values/emails/passwords if needed),
  • Describe all options and toggles enabled or changed,
  • Include any files or environmental changes,
  • Identify the expected and actual result at each stage,
  • Ensure any reasonably skilled user can follow and hit the same issue.

Expected Behavior

Leaving function_name_filter_list empty should allow all tool functions.

Actual Behavior

Leaving function_name_filter_list empty causes

2025-11-25 15:48:34.472 | DEBUG    | open_webui.utils.middleware:process_chat_payload:1452 - 'list' object has no attribute 'split'

This leads to the message "Failed to connect to MCP server 'TOOL_ID'" upon submitting a chat message to a model with the tool enabled.

Steps to Reproduce

  1. Add an External Tool (Admin Panel > Settings > External Tools). I was creating an MCP tool, not an Open API tool, though I doubt that's relevant.
  2. Leave "Function Name Filter List" empty
  3. Save
  4. Configure a model to have that tool enabled (Admin Panel > Settings > Models), edit model, check box next to tool, click "Save & Update"
  5. Start chat with model from step 4
  6. Note "Failed to connect to MCP server 'TOOL_ID'" error message

Logs & Screenshots

If you have debug logs turned on, you'll notice on server side:

2025-11-25 15:48:34.472 | DEBUG    | open_webui.utils.middleware:process_chat_payload:1452 - 'list' object has no attribute 'split'

Additional Information

No response

Originally created by @kathrynalpert on GitHub (Nov 25, 2025). Original GitHub issue: https://github.com/open-webui/open-webui/issues/19486 ### Check Existing Issues - [x] I have searched for any existing and/or related issues. - [x] I have searched for any existing and/or related discussions. - [x] I have also searched in the CLOSED issues AND CLOSED discussions and found no related items (your issue might already be addressed on the development branch!). - [x] I am using the latest version of Open WebUI. ### Installation Method Docker ### Open WebUI Version v0.6.40 ### Ollama Version (if applicable) _No response_ ### Operating System Debian Bookworm (Docker: python:3.11-slim-bookworm) ### Browser (if applicable) _No response_ ### Confirmation - [x] I have read and followed all instructions in `README.md`. - [x] I am using the latest version of **both** Open WebUI and Ollama. - [x] I have included the browser console logs. - [x] I have included the Docker container logs. - [x] I have **provided every relevant configuration, setting, and environment variable used in my setup.** - [x] I have clearly **listed every relevant configuration, custom setting, environment variable, and command-line option that influences my setup** (such as Docker Compose overrides, .env values, browser settings, authentication configurations, etc). - [x] I have documented **step-by-step reproduction instructions that are precise, sequential, and leave nothing to interpretation**. My steps: - Start with the initial platform/version/OS and dependencies used, - Specify exact install/launch/configure commands, - List URLs visited, user input (incl. example values/emails/passwords if needed), - Describe all options and toggles enabled or changed, - Include any files or environmental changes, - Identify the expected and actual result at each stage, - Ensure any reasonably skilled user can follow and hit the same issue. ### Expected Behavior Leaving `function_name_filter_list` empty should allow all tool functions. ### Actual Behavior Leaving `function_name_filter_list` empty causes ``` 2025-11-25 15:48:34.472 | DEBUG | open_webui.utils.middleware:process_chat_payload:1452 - 'list' object has no attribute 'split' ``` This leads to the message `"Failed to connect to MCP server 'TOOL_ID'"` upon submitting a chat message to a model with the tool enabled. ### Steps to Reproduce 1. Add an External Tool (Admin Panel > Settings > External Tools). I was creating an MCP tool, not an Open API tool, though I doubt that's relevant. 2. Leave "Function Name Filter List" empty 3. Save 4. Configure a model to have that tool enabled (Admin Panel > Settings > Models), edit model, check box next to tool, click "Save & Update" 5. Start chat with model from step 4 6. Note `"Failed to connect to MCP server 'TOOL_ID'"` error message ### Logs & Screenshots If you have debug logs turned on, you'll notice on server side: ``` 2025-11-25 15:48:34.472 | DEBUG | open_webui.utils.middleware:process_chat_payload:1452 - 'list' object has no attribute 'split' ``` ### Additional Information _No response_
GiteaMirror added the bug label 2026-04-25 08:25:04 -05:00
GiteaMirror commented 2026-04-25 08:25:06 -05:00
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@tjbck commented on GitHub (Nov 25, 2025):

.41 will be released shortly!

<!-- gh-comment-id:3577815945 --> @tjbck commented on GitHub (Nov 25, 2025): .41 will be released shortly!
GiteaMirror commented 2026-04-25 08:25:08 -05:00
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@silentoplayz commented on GitHub (Nov 26, 2025):

Just stopping by to mention that I experienced this same issue early this morning!

Image

I am also able to confirm that this bug has been solved on the dev branch.

<!-- gh-comment-id:3578781408 --> @silentoplayz commented on GitHub (Nov 26, 2025): Just stopping by to mention that I experienced this same issue early this morning! <img width="2299" height="914" alt="Image" src="https://github.com/user-attachments/assets/9c20beb1-3d90-45a3-97c6-e0ccc47ed3fa" /> I am also able to confirm that this bug has been solved on the dev branch.
GiteaMirror commented 2026-04-25 08:25:08 -05:00
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@impiyush commented on GitHub (Nov 26, 2025):

came here to mention that I ran into the same issue today when setting up a tool server from the admin settings. Looking forward to the .41 update to get this resolved.

<!-- gh-comment-id:3579768047 --> @impiyush commented on GitHub (Nov 26, 2025): came here to mention that I ran into the same issue today when setting up a tool server from the admin settings. Looking forward to the .41 update to get this resolved.
GiteaMirror commented 2026-04-25 08:25:09 -05:00
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@aleixdorca commented on GitHub (Nov 26, 2025):

Good morning, I turned on DEBUG log level and saw the same problem. I started a discussion about MCP not working. I guess it all comes down to this issue. Thanks!

<!-- gh-comment-id:3579836001 --> @aleixdorca commented on GitHub (Nov 26, 2025): Good morning, I turned on DEBUG log level and saw the same problem. I started a discussion about MCP not working. I guess it all comes down to this issue. Thanks!
GiteaMirror commented 2026-04-25 08:25:10 -05:00
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@MordiSacks commented on GitHub (Nov 26, 2025):

same issue here with external tool server

<!-- gh-comment-id:3580220851 --> @MordiSacks commented on GitHub (Nov 26, 2025): same issue here with external tool server
GiteaMirror commented 2026-04-25 08:25:10 -05:00
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@imranali4 commented on GitHub (Nov 26, 2025):

Same issue here. For now the work around that worked for me is to just add a “,” single comma in the filter list in the external tool server settings.

<!-- gh-comment-id:3580561179 --> @imranali4 commented on GitHub (Nov 26, 2025): Same issue here. For now the work around that worked for me is to just add a “,” single comma in the filter list in the external tool server settings.
GiteaMirror commented 2026-04-25 08:25:11 -05:00
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@Classic298 commented on GitHub (Nov 26, 2025):

Fixed in dev guys, as tim said - .41 will be released soon :)

<!-- gh-comment-id:3581029538 --> @Classic298 commented on GitHub (Nov 26, 2025): Fixed in dev guys, as tim said - .41 will be released soon :)
GiteaMirror commented 2026-04-25 08:25:11 -05:00
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@tomkho123 commented on GitHub (Nov 30, 2025):

Most of my tools don't have that issue except one... So I just disabled that tool (for some models only)

<!-- gh-comment-id:3592261246 --> @tomkho123 commented on GitHub (Nov 30, 2025): Most of my tools don't have that issue except one... So I just disabled that tool (for some models only)
GiteaMirror commented 2026-04-25 08:25:13 -05:00
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@aimendenche-nw commented on GitHub (Dec 1, 2025):

Hello @Classic298, do you have any idea when the .41 will be released ?

<!-- gh-comment-id:3595435763 --> @aimendenche-nw commented on GitHub (Dec 1, 2025): Hello @Classic298, do you have any idea when the .41 will be released ?
GiteaMirror commented 2026-04-25 08:25:14 -05:00
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@Classic298 commented on GitHub (Dec 1, 2025):

@aimendenche-nw very soon afaik. No EXACT timeline but it should be close. The majority of what is planned for .41 is done.

<!-- gh-comment-id:3595484928 --> @Classic298 commented on GitHub (Dec 1, 2025): @aimendenche-nw very soon afaik. No EXACT timeline but it should be close. The majority of what is planned for .41 is done.
GiteaMirror commented 2026-04-25 08:25:16 -05:00
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@Classic298 commented on GitHub (Dec 1, 2025):

Since this is fixed in dev, @silentoplayz can this be closed?

<!-- gh-comment-id:3595526339 --> @Classic298 commented on GitHub (Dec 1, 2025): Since this is fixed in dev, @silentoplayz can this be closed?
GiteaMirror commented 2026-04-25 08:25:17 -05:00
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@silentoplayz commented on GitHub (Dec 1, 2025):

Since this is fixed in dev, @silentoplayz can this be closed?

Would like more confirmation here that this issue has been solved on the dev branch (or in the next version release) before closing this one out.

Edit: Closing this out now actually, as a workaround was determined by @imranali4 with https://github.com/open-webui/open-webui/issues/19486#issuecomment-3580561179.

<!-- gh-comment-id:3595892530 --> @silentoplayz commented on GitHub (Dec 1, 2025): > Since this is fixed in dev, [@silentoplayz](https://github.com/silentoplayz) can this be closed? Would like more confirmation here that this issue has been solved on the `dev` branch (or in the next version release) before closing this one out. Edit: Closing this out now actually, as a workaround was determined by @imranali4 with https://github.com/open-webui/open-webui/issues/19486#issuecomment-3580561179.
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Reference: github-starred/open-webui#34427
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