Building an AI Coding Agent from Scratch with Claude Agent SDK

You've been using Claude as a chatbot — paste code, get a reply, paste again. That works. But there's a different mode entirely: give Claude a set of tools and a goal, and let it figure out the steps itself.

That's what an agent is. Not a smarter autocomplete — a loop that reads files, runs checks, makes decisions, and calls your code until the job is done.

In this article, I'll walk through building a TypeScript code review agent using Anthropic's SDK. It will autonomously scan your project, find issues, and output a structured report — without you prompting it at each step.

What Makes Something an "Agent"

A regular API call is stateless: you send a prompt, you get a response.…