Start here. Register tools with @mcp.tool(); the SDK infers the JSON input schema from type hints, the output schema from the return annotation, and returns structuredContent alongside text. ToolAnnotations carries behavioural hints (readOnlyHint, idempotentHint) the host can show to users. The client lists tools, inspects schemas + annotations, calls both, and asserts structured output.

# stdio (default — the client spawns the server as a subprocess)
uv run python -m stories.tools.client

# HTTP — the client self-hosts the server on a free port, runs, then tears it down
uv run python -m stories.tools.client --http
# same, against the lowlevel-API server variant
uv run python -m stories.tools.client --http --server server_lowlevel

• server.py calc — Literal[...] and BaseModel in the signature become the tool's inputSchema / outputSchema with zero hand-written JSON.
• server.py echo — structured_output=False opts out of schema inference for a plain text-only tool.
• server_lowlevel.py — the same wire contract built by hand: this is what MCPServer generates for you.

Tools — server features

schema_validators/ (every input-schema source: pydantic / TypedDict / dataclass / dict), error_handling/ (is_error vs protocol error), streaming/ (progress mid-call).