Invalid 'tools[12].function.name': string too long.

[vizo]

What happened?

In line

LibreChat/packages/api/src/mcp/MCPManager.ts

Line 160 in 7a9a99d

const pluginKey = `${tool.name}${CONSTANTS.mcp_delimiter}${serverName}`;

every tool from a plugin MCP server automatically gets the suffix _mcp_${server_name}.

This seems problematic when using publicly available MCP tools.

I received the following error by ChatGPT 4:

Something went wrong. Here's the specific error message we encountered:
An error occurred while processing the request: 
400 Invalid 'tools[12].function.name': string too long. 
Expected a string with maximum length 64, but got a string with length 71 instead.

However, tool name was actually only 54 characters long.

Some discussions about it: https://www.reddit.com/r/mcp/comments/1mcf0ig/whats_the_maximum_length_of_a_tool_name/#:~:text=Do%20you%20limit%20your%20tool,for%20the%20sake%20of%20interoperability.

I think it should be up to the MCP provider to add prefixes or suffixes to tool names. LibreChat should only apply a prefix/suffix if explicitly configured in the YAML under a specific MCP server (e.g., prefix_functions_with: or suffix_functions_with:).

Version Information

ghcr.io/danny-avila/librechat-dev                latest                    3cb311226866   4 days ago      1.57GB
ghcr.io/danny-avila/librechat-rag-api-dev-lite   latest                    d813432c9b0a   2 weeks ago     1.68GB
ghcr.io/danny-avila/librechat                    latest                    fdaddca5d75c   2 weeks ago     1.57GB


### Steps to Reproduce

1. Add tools.
2. Write anything in chat, ChatGPT will response with an error.

### What browsers are you seeing the problem on?

Chrome

### Relevant log output

```shell
chat-meilisearch  | 2025-09-15T14:38:02.973173Z  INFO HTTP request{method=POST host="meilisearch:7700" route=/indexes/messages/documents query_parameters= user_agent=node status_code=202}: meilisearch: close time.busy=1.70ms time.idle=3.58ms
chat-meilisearch  | 2025-09-15T14:38:02.977374Z  INFO HTTP request{method=GET host="meilisearch:7700" route=/indexes/convos/documents/8cd3c65c-b161-46af-8ea6-184077e2f0ec query_parameters= user_agent=node status_code=200}: meilisearch: close time.busy=3.74ms time.idle=301µs
chat-meilisearch  | 2025-09-15T14:38:03.031795Z  INFO index_scheduler::batch: document indexing done indexing_result=DocumentAdditionResult { indexed_documents: 1, number_of_documents: 125 } processed_in=58.661337ms
chat-meilisearch  | 2025-09-15T14:38:03.039701Z  INFO index_scheduler: A batch of tasks was successfully completed with 1 successful tasks and 0 failed tasks.
LibreChat         | 2025-09-15 14:38:03 error: [api/server/controllers/agents/client.js #sendCompletion] Operation aborted 400 Invalid 'tools[12].function.name': string too long. Expected a string with maximum length 64, but got a string with length 71 instead.
LibreChat         | 2025-09-15 14:38:03 error: [api/server/controllers/agents/client.js #sendCompletion] Unhandled error type 400 Invalid 'tools[12].function.name': string too long. Expected a string with maximum length 64, but got a string with length 71 instead.

Screenshots

No response

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[danny-avila]

The current design is necessary to prevent collision within LC.

While you may not be in control of the public MCP server, you can reduce the serverName length at your discretion since this is configured in the YAML:

mcpServers:
  name: # this unique key value `name` gets used as part of the tool name `serverName`
    type: http
    url: "http://0.0.0.0:8000/mcp"

In your case, a 4-letter configured server name will keep you at 64 characters for this tool.

Of course some optimizations here are in order (all possible):

• Customizing the display name
• Customizing how specific tools are mapped for the API calls
• Changing the delimiter, i.e. _m_ instead of _mcp_

[vizo]

Thanks for you response.

May i ask why there is a need for delimiter in current design, if we exactly know the suffix (name)?

Thank you.