Start with a small Python contract.
Define one tool with a useful name, typed arguments, a narrow data source, and a result a user can verify. FastMCP's decorators make registration approachable, but the framework cannot decide whether the tool should read, write, or require approval.
Keep the first handler deterministic enough to test. A local weather lookup, a read-only service catalog, or a controlled calculation lets the article focus on MCP behavior before it introduces credentials and irreversible side effects.
Understand how the process runs.
Use the documented FastMCP runner for local development and keep protocol output separate from diagnostics. When the server uses stdio, writing ordinary logs to stdout can break the connection. Send diagnostics to stderr and make the startup command reproducible.
HTTP execution changes the exposure and lifecycle. Before sharing an endpoint, document the transport, authentication, origin or host assumptions, request limits, and the path for stopping or rotating the server.
- Use local execution while learning the tool contract.
- Test startup, discovery, a successful call, and a failed call.
- Treat HTTP deployment as a security and operations decision.
Test the tool outside the happy path.
Call the tool with missing arguments, wrong types, unexpected values, and an unavailable dependency. Confirm that the server returns a useful error without leaking a credential, stack trace, or internal path that the client does not need.
Use MCP Inspector or a compatible client to verify the advertised schema. Keep the version of FastMCP, Python, and dependencies with the test notes because the framework and protocol documentation evolve.
Make the example ready for a real owner.
A framework tutorial becomes operationally useful when it explains who owns the data, which credentials the process uses, how the result is verified, and what happens when the upstream system is unavailable. Add those boundaries before adding more tools.
If the server needs to reach production data, create a separate environment and a least-privilege identity for the first integration. The shortest code path is not automatically the safest operating path.