Serena + ChatGPT Developer Mode via Cloudflare Tunnel produces error messages on /mcp

[Alexei-WLU]

Hi, I’m trying to use Serena as an MCP server for ChatGPT in Developer Mode and I’m seeing the tunnel produces error messages during MCP use after the request reaches the Serena endpoint. To clarify: I am not saying the connection drops or that ChatGPT disconnects. So it might be some ChatGPT compatibility

Environment

• Windows 10 + WSL2 Ubuntu
• Cloudflare Tunnel
• Serena started with streamable-http
• Public endpoint: https://mcp.alexshshsh.com/mcp
• Local origin: http://localhost:8000

Serena start command

uvx --from git+https://github.com/oraios/serena \
  serena start-mcp-server \
  --transport streamable-http \
  --port 8000 \
  --context chatgpt \
  --project /home/alex/myproject

Cloudflare behavior
ChatGPT Developer Mode connects, but Cloudflare logs repeated errors like:

ERR error="stream 1 canceled by remote with error code 0" connIndex=1 event=1 ingressRule=0 originService=http://localhost:8000
ERR Request failed error="stream 1 canceled by remote with error code 0" connIndex=1 dest=https://mcp.alexshshsh.com/mcp event=0 ip=198.41.220.65 type=http

This repeats with different stream IDs and Cloudflare IPs.

Serena behavior
Serena appears to start correctly:

• MCP server starts
• StreamableHTTP session manager starts
• Uvicorn listens on 0.0.0.0:8000
• Pyright initializes successfully for the project

So the issue seems to be during MCP connection/handshake rather than Serena startup.

Questions

1. Has Serena been tested with ChatGPT Developer Mode using native MCP over streamable-http?
2. Is /mcp with --transport streamable-http the correct setup for ChatGPT Developer Mode?
3. Are there known issues with Serena behind Cloudflare Tunnel?
4. Is any extra Serena-side configuration needed for ChatGPT Developer Mode beyond --transport streamable-http, --context chatgpt, and exposing /mcp over HTTPS?

I can provide full logs and tunnel config if useful.

[MischaPanch]

Hi @Alexei-WLU . I tested the connection when I wrote the instructions in our docs for that case, chatgpt was not supporting MCP back then, so I suggested using mcpo. See here.

A lot has happened since and the core team has not tried doing that recently (since codex cli/app is a better pathway to this for us). Maybe someone from the community can chip in. You can also try the mcpo route.

Ofc, the error might be due to firewall or something else

[Alexei-WLU]

@MischaPanch ,
It does not fail entirely. With my setup (i.e. MCP), Serena appears to be communicating with ChatGPT and working somehow more or less. So it might be some ChatGPT compatibility

[itxashancode]

But the error "stream 1 canceled by remote with error code 0" indicates that the remote (Serena) reset the stream with error code 0 (which is NO_ERROR). In HTTP/22.

[Alexei-WLU]

Are you saying that such messages ("stream 1 canceled by remote with error code 0") should be treated as normal information messages (not exceptions or warnings)? And Serena is functioning normally in this case, as expected?

[itxashancode]

Not exactly, they're not purely informational, but they're also not necessarily a sign that Serena is broken.

error code 0 in HTTP/2 means NO_ERROR, which means the stream was closed cleanly from the remote side, not crashed or rejected. Cloudflare logs it as ERR because it sees an unexpected RST_STREAM frame, but the underlying cause is usually just ChatGPT closing the connection after it gets what it needs (or during polling/keepalive cycles).

So the practical answer is: if Serena is responding to tool calls correctly and ChatGPT is functioning as expected, these log lines are noise you can ignore. They reflect ChatGPT's connection behavior, not a Serena failure.

The real signal to watch for is whether actual MCP tool calls succeed or fail. If tools are being called and returning results, Serena is working fine. If calls time out or return errors, then something deeper is wrong and the full logs would help narrow it down.