読み込みとツール一覧を確認する

Your server runs, but how do you know it's healthy? Let's verify that it loads and that your tool shows up where clients can see it. 🔍

The SDK ships a helper for this. Running mcp dev on your file launches the server with a visual inspector attached.

That opens the MCP Inspector in your browser: a friendly panel for poking at your server without writing any client code.

In the Inspector you click Connect. That runs the handshake; if it succeeds, your server loaded and is speaking MCP correctly.

Now switch to the Tools tab. This calls the protocol's list operation and shows every tool your server advertises.

You should spot your function there by name, like "hello" or "greet", alongside the description that came from its docstring.

Click the tool and the Inspector shows its schema, the typed parameters FastMCP built from your hints. This is what the model reads.

Fill in any arguments and hit run. The Inspector invokes your tool and shows the exact result the model would receive back.

If the Tools list is empty, your decorator probably didn't run. Make sure @mcp.tool() sits directly above the function.

That tab is just a UI over a real message: the client sends a tools/list request and your server replies with the catalog.

The Inspector isn't only for tools. It has tabs for resources and prompts too, so you can verify every capability your server exposes.

What does the Inspector's Tools tab actually do under the hood?

You launched mcp dev, connected in the Inspector, saw your tool listed, and even called it live. Your first server is real and verified. Congrats! 🎉