MCP Server and Warp Terminal, Connection Issue

[Dean_Wittmann]

I've enabled the MCP Server in About Plugins in Qt Creator 19.0.0 and I can connect to it via the MCP Inspector via this command in a command prompt window:

npx @modelcontextprotocol/inspector

which downloads and initiates the MCP Inspector in your browser. I was successful in connecting and using tools to open a file in Qt Creator.

When I add this JSON configuration in Warp's Settings / MCP Servers / Add:

{
"QtCreator": {
"type": "sse",
"url": "http://127.0.0.1:3001/sse"
}
}

and Save the MCP Server configuration with the Save button, I get this error on the screen and in the log:

2026-04-02 19:30:14.785 | [error] MCP: Failed to connect to server: Transport creation error: Unexpected status code: 204 No Content

Any help would be appreciated.

[davecotter]

well, i use Cursor, so i do NOT know if it is the exact same config, but what i have in Cursor is this:

    "qt-creator": {
      "url": "http://localhost:3001",
      "transport": "http"
    },

[Dean_Wittmann]

Thanks Dave,
I tried your suggestion and it still gives me the same error. I think it's expecting a reply that it's not getting. Warp Terminal is not just a terminal, it is the glue that ties your MCP Server to the LLM's. It supports multiple LLM's and is a terminal / IDE environment.

[cristian-adam]

See the comments of Qt Creator 19 released for details of a possible workaround.

钟勇
After testing, it turned out that the real reason is quite simple: VSCode does not support MCP servers using the SSE protocol.
However, it does support HTTP. Therefore, I had Copilot write a proxy (Streamable HTTP ↔ SSE), and now VSCode can interact with QtCreator normally.

VS Code uses the Streamable HTTP protocol (sending requests via POST and receiving results in the HTTP response body), while Qt Creator uses the SSE protocol (establishing an event stream via GET, sending requests via POST, and receiving responses asynchronously through the SSE stream).

What the proxy does:

On startup: Establishes a persistent SSE connection with Qt Creator, with a background thread continuously reading the event stream and routing responses to the corresponding waiters based on their id.

When receiving a POST request from VS Code:

Parses the JSON-RPC message and extracts the id.

Forwards it to Qt Creator (POST /sse).

If there is an id (it's a request): Blocks and waits for the response with the matching id in the SSE stream, then returns it as the HTTP response body to VS Code.

If there is no id (it's a notification): Forwards it directly and returns a 202.

When receiving a GET request from VS Code: Provides an SSE stream and forwards notifications actively pushed by Qt Creator.

In short: VS Code [Streamable HTTP] ↔ Proxy ↔ [SSE] Qt Creator

Alternatively you can try Qt Creator 20 snapshots. In Qt Creator 20 we rewrote the network connection part. We also have now an ACP Client that allows you to chat with any of these ACP compatible agents e.g. Claude Agent, Cursor, Codex CLI, or OpenCode.

Lastly Thank you @davecotter for the initial work with the mcp server plugin. Without this we wouldn't have all of this. 🙏

[davecotter]

this is what i did, and it started working. first make a local branch of my mcp project, i put it at Z:\depot.
build and install the mcp plugin, then run Qt Creator. when it is running, then issue this command: