modelcontextprotocol / modelcontextprotocol/python-sdk
FastMCP.run(transport="stdio") produces noisy traceback on KeyboardInterrupt instead of clean exit
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Description
Initial Checks
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Description
Running a FastMCP stdio server from the terminal and interrupting with Ctrl-C produces a multi-frame traceback through anyio.run() → asyncio.runners → mcp.server.lowlevel.server.run → anyio.streams.memory.receive. The server is correctly waiting on stdin in an async loop; the trace surfaces because anyio/asyncio don't suppress the cancellation chain. Suggested fix: catch KeyboardInterrupt (or asyncio.CancelledError at the outer boundary) inside FastMCP.run and exit cleanly. Cosmetic but reduces user confusion when testing MCP servers from the terminal.
Example Code
Python & MCP Python SDK
Python 3.13.5
MCP Python SDK 1.27.1
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the Ctrl-C behavior for a FastMCP stdio server, then trace FastMCP.run through mcp.server.lowlevel.server.run and the anyio memory receive path. The fix is done when interrupting the server exits cleanly without a traceback while normal shutdown behavior remains unchanged.
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Assessment
- Tech stack
- python
- Domain
- backend, cli
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 64/100