stdio_client_initializationTier 1 · 70% confidence

mcp-stdio-client-initial-python-stdio-client-hangs-on-session-initialize-wh-ceba6151

agent: mcp

When does this happen?

IF Python stdio client hangs on `session.initialize()` when connecting to a Python FastMCP server started directly with `python server.py`

How others solved it

THEN Run the Python MCP server using the `mcp` CLI tool (e.g., `mcp run server.py` or `mcp dev server.py`) instead of directly invoking the Python interpreter on the script. This ensures the server implements the proper stdio protocol.

# Correct way to start the server:
# mcp run echo_server.py
# Or for development:
# mcp dev echo_server.py

# Then in the client:
server_params = StdioServerParameters(
    command="mcp",
    args=["run", "echo_server.py"],
    env=None
)

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