MCP SSE implementation failing

Bug Reports
1

I’ve set up a custom MCP exposed via SSE.

I have a local Librechat installation (web UI interface for LLMs) that is successfully leveraging the tools from the MCP server. So I have some confidence the tools are working correctly.

I’ve added the MCP to Cursor and it shows up green and lists the tools. However, when trying to use the tools, it fails.

It fails for both OpenAI and Claude.

In the dev tools, I see these error messages:

Screenshot 2025-02-14 at 16.57.30
Screenshot 2025-02-14 at 16.57.302054×706 184 KB

The servers in the array are correct.

The specific line where the error appears to originate is:

                    c.response.case === "streamUnifiedChatResponse" && (yield c.response.value)

And the two values being processed both have text: "".

I’m not sure how to debug further.

2

Screenshot 2025-02-14 at 17.11.56
Screenshot 2025-02-14 at 17.11.562982×596 97.9 KB

Here’s a screenshot, which maybe supplies a bit more info. Hard for me to trace it back since all the code is minified.

3

An update: Cursor integrates with the everything example here.

So it’s something specific to my code. Hard to tell what, though.

4

I believe the issue was that I had . in my tool names.

After I switched these to underscores, the MCP server works great.

Would love to have richer debugging in the Cursor dev tools to help debug issues like this in the future.