Inspect the Connection

The server is useful only when a client can initialize a session, discover the tool, and invoke it successfully. Use the SDK development command to launch MCP Inspector:

uv run mcp dev server.py

The command imports the module, finds the mcp server object, launches it over stdio, and opens the Inspector development interface.

Verify the protocol flow

In Inspector:

1. Connect to the server.
2. Open the Tools section.
3. Confirm that add appears with integer fields for a and b.
4. Invoke it with a = 2 and b = 3.
5. Confirm that the result contains 5.

You have now exercised the essential path: initialization, capability negotiation, tool discovery, tool invocation, and a structured result.

Diagnose the common failures

• If the module cannot be imported, run the command from the project directory and recheck the filename.
• If the tool is missing, confirm that @mcp.tool() decorates the function attached to the same mcp instance.
• If the stdio connection breaks, remove ordinary print() calls from server code.