Custom MCP server connection fails: Only GET / requests

ChatGPT Bugs
,
1

Hi,

I’m trying to connect a custom MCP server (implemented in Node.js/Express with @modelcontextprotocol/sdk/server/streamableHttp.js) to ChatGPT as a connector. The MCP endpoint is mounted at /sse, and I’ve set the connector URL explicitly to https://test.gurum.cat/sse.

Environment

  • MCP server: Node.js + Express + @modelcontextprotocol/sdk/server/streamableHttp.js

  • Endpoint: https://test.gurum.cat/sse

  • Connector config: no authentication

Problem

  • When I attempt to connect the server, the connector always shows “Connection failed.”

  • Looking at the server logs, I never receive a POST /sse initialize request. Instead, I only see repeated GET / requests (and GET /favicon.*).

    [HTTP] -> GET /
[HTTP] <- GET / 200
[HTTP] -> GET /
[HTTP] <- GET / 200

  • The /sse endpoint itself works fine. When I manually send a POST /sse with an initialize request via curl, the session is created successfully and tools/list works as expected.

  • In the mcp inspector, both fetch and search methods were found to work normally.

  • However, since the connector never actually calls /sse, the MCP initialization never starts, no session is created, and the connector UI just fails.

My questions

  1. Is it expected that the connector only performs GET / checks and never attempts to call the actual MCP endpoint (/sse)?

  2. Could the connector be failing at the health-check step and not proceeding to initialization at all?

  3. Given that my MCP implementation at /sse works with manual requests, what could cause ChatGPT’s connector backend to never hit /sse in the first place?

Any guidance or examples of a working MCP server setup would be greatly appreciated.

2

Same issue. Very frustrating. Lots of trouble

3

I’ve found that the ChatGPT client makes requests to https://your.domain.com/, that is, the resource at /. You can see this [HTTP] -> GET /. I set my MCP server to serve at / instead of /mcp or /sseand it works.

4

So, I was able to get it working for only a very period of time. Since then I have long to find the magic formula to get it working again and I’m starting to believe that it’s impossible because chat GPT must have permanently associated A client ID with my domain and I’ve lost that ID so I don’t really know what to do at this point unless I have to go get an entirely new domain because this one’s just tainted. This has been such an ordeal and having experienced five minutes of it working is making it even worse, I must figure this out, claude works no problem with the same exact thing