Claude Agent SDK: Custom Tools with In-Process MCP
Summary
Add custom Python tools to Claude agents with one decorator. No server. No HTTP. Just code.
Most agent frameworks make tool-calling sound complex: spin up an MCP server, expose HTTP endpoints, wire up a transport, then connect a client. The Claude Agent SDK for Python flips that. You define a tool with a decorator, register it with one helper, and your agent calls Python functions directly — no separate process, no network hop.
This guide walks through building a working agent with two custom in-process tools. By the end, you will know how to expose any Python function to Claude, validate inputs with type hints, and ship the whole thing in a single file.
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