MCP server: the tool registry returned an error saying no tools were defined

ChatGPT Apps SDK
1

I’m trying to update a MCP server, which apparently can’t be updated with a Business account. So in creating a new one, it is unable to access to the tools. It says:

the tool registry returned an error saying no tools were defined under that path

Of course there’s no other errors, ChatGPT doesn’t even seem to be calling the mcp server at all. Is there a way to debug that?

2

FWIW, I built a chat bot using openai API, which is able to look at the same mcp server that chatGPT fails to see, so the problem is not on the mcp server side.

3

I’d first suspect the ChatGPT app registration/config

That error sounds like ChatGPT is looking at the wrong MCP path or stale tool metadata. you should confirm the server is running and that ChatGPT is connected to the /mcp endpoint.

Confirm the exact MCP URL in ChatGPT, including /mcp

Refresh the app/connector metadata if in developer mode

Re-scan and publish a new app version if it is already published

4

I would debug this as a discovery/registration problem first, not a tool implementation problem.

A quick checklist:

  1. Confirm the exact URL ChatGPT is using, including the path. If your server exposes tools under `/mcp`, do not test only the base host.
  2. Compare the discovery response that your API client sees with what the ChatGPT app registration points at. It is possible for the server to be healthy while the app points at an old path.
  3. Change one visible tool name or description and republish/rescan the app. If ChatGPT still shows the old metadata or no tools, you are looking at stale registration/cache rather than runtime execution.
  4. Add request logging at the reverse proxy edge. If ChatGPT never hits the server during scan, the failure is before MCP runtime.
  5. Make sure the published app version and the developer/test version are not using different connector URLs.

The useful signal is whether a scan produces any inbound request at all. No request means registration/path/auth. Request with an empty tools result means server discovery/schema.