[Enhancement]: Respond to the notifications/tools/list_changed MCP message

[squidmarks]

What features would you like to see added?

Respond to notifications/tools/list_changed notification MCP message

More details

It appears that Librechat is not responding to the notifications/tools/list_changed notification message sent from an MCP server. This message is sent when the tools list changes after the connection is established. The MCP client should respond by requesting the tool list as described in the MCP List Changed Notification Specification

My MCP server is dynamically creating new tools and sending list_changed notifications, but LibreChat is not requesting a new tool list, so the tool list remains static until a restart is done.

Thanks.

Geoff

Which components are impacted by your request?

No response

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[danny-avila]

Which MCP servers/tools are you using that actively do this?

[squidmarks]

I'm rolling my own. We have an MCP server that provides an interface to laboratory equipment. Rather than publish all tools/actions that could possibly be used (i.e. all the actions that could be done on a particular instrument device), there is a use-instrument tool that the user can call ("I want to use the QC pH meter"), that tool will then dynamically generate a tool for each action that instrument can perform. After executing the "use-instrument" tool, the user shoudl then be able to say "Whats the pH?" and it would execute the "qc_ph_meter_read_ph" tool. But, this does not currently work with LibreChat b/c it does not respond to the tool list change notification that is emitted after a new tool is dynamically added, so its unaware that a new tool has been added.

I am giving a very simple use-case, but there are many other examples where dynamic/custom tool creation is useful. I think this was the intent behind why the tool list change notification was provided in the MCP specification.

Thanks!

Geoff

[danny-avila]

Understood @squidmarks

A minimum reproduction would help me get started, thanks for the report.

[squidmarks]

The basic flow is shown here in the specification: https://modelcontextprotocol.io/specification/2025-03-26/server/tools#list-changed-notification.
Subscribe to the tool list updated message:
{
"jsonrpc": "2.0",
"method": "notifications/tools/list_changed"
}

...then ask for an updated list.

I could probably put together a simple mcp server that has one tool (add_new_tool) that adds a new tool to the mcp tools list, then publishes a list_change message. Let me know if that is necessary for testing.

Geoff

[danny-avila]

I could probably put together a simple mcp server that has one tool (add_new_tool) that adds a new tool to the mcp tools list, then publishes a list_change message. Let me know if that is necessary for testing.

Yeah that would be helpful, for myself or anyone else who would take this on

[scitara-cto]

Here's a test mcp server that can be used to develop/test the capability to work with an mcp server that dynamically creates tools. This mcp server allows a tool to be added dyamically using the add_tool tool. When a new tool is added, the mcp server will notify all connected clients that the tool list has changed. Clients should respond to this notification by requesting the tool list.

https://github.com/scitara-cto/dynamic-tool-mcp-server

If you point me in the right direction, I can probably add this feature to LibreChat.

Geoff

[scitara-cto]

It looks like the mcp sdk does not have support for this, yet, but there is a PR under review that will add it. Once the sdk supports it, I suspect merging in the updated sdk will bring support for auto-updating tools for free.
modelcontextprotocol/typescript-sdk#239

[matthisholleville]

@danny-avila Couldn't we re-call the initialization of tools at regular intervals? It's complicated to have to restart LibreChat every time we update the MCP servers.

[scitara-cto]

@danny-avila Couldn't we re-call the initialization of tools at regular intervals? It's complicated to have to restart LibreChat every time we update the MCP servers.

This isn't really something that LibraChat should implement. The base MCP Typescript library needs to be updated to support dynamic tool updates (the MCP protocol specifies a server can publish a "tool list changed" message, the MCP client should automatically retrieve the new list when it receives this event message, currently it doesn't). There is an issue here outstanding to support this: modelcontextprotocol/typescript-sdk#239. Once this is implemented, updating LibreChat with the updated Typescript MCP library should bring in dynamic tool support.

[matthisholleville]

Discovering a change in the tools is only part of what I'm referring to.

If Librechat fails to contact the MCP server at startup, it never retries. To do this, you need to restart its startup cycle.

Furthermore, I agree that the SDK needs to evolve, however, in the meantime this seems to be an inexpensive solution.

[mboret]

It's also necessary when creating an MCP server with customUserVars, when the required variable is an API/Access token to the MCP Server. A tools list request should be done, otherwise, the MCP Server is unusable.

[matthisholleville]

@mboret I’m not entirely convinced. Initializing the connection doesn’t necessarily require an API key or any authentication method; its sole purpose is to fetch the full list of available tools. It’s then up to the MCP server to enforce authentication—via middleware—before each tool is actually invoked.

That’s exactly how we’ve implemented it, and it works flawlessly. In fact, it mirrors the standard approach used by basic REST APIs.