What is this?

Claude Code in 30 seconds

Claude Code is Anthropic’s terminal-based AI coding assistant. You run claude in your shell, describe what you want in plain language, and it reads your code, edits files, and runs commands until the job is done.

It is not a chatbot you only talk to—it is an AI agent that can actually do work.

What this site covers

In March 2026, people noticed that Claude Code’s npm package accidentally shipped source map files. Using those maps, the community reconstructed roughly 1,884 TypeScript source files—essentially the full internal implementation.

This site uses that reconstructed code to explain, in plain language:

What is the core idea behind Claude Code? (Simpler than you might think.)
How does it let the AI operate your machine? (The tool system.)
How does it stay safe? (A five-layer permission model.)
How is context managed? (Compaction and related strategies.)
What can you learn—and can you build something like it yourself? (Yes.)

What you do not need

You do not need to have read Claude Code’s source before.
You do not need prior experience building AI agents.
You do not need to know TypeScript (we use pseudocode and diagrams).
You do need to be a developer with basic programming literacy.

What is in this repo?

claude-code-sourcemap/
├── package/                   ← Raw npm package output
│   ├── cli.js                 ← ~13MB bundled executable
│   └── cli.js.map             ← ~60MB source map (where the TS came from)
├── restored-src/src/          ← Reconstructed TypeScript sources
│   ├── main.tsx               ← Program entry
│   ├── QueryEngine.ts         ← Query engine (core)
│   ├── Tool.ts                ← Tool type definitions
│   ├── tools/                 ← 30+ tool implementations
│   └── services/              ← API, MCP, and other services
└── docs/                      ← This tutorial site

Important

This repository does not build or run as a full product. There is no complete build setup and dependencies are incomplete. Treat it as read-only learning material, not something you can compile into a working Claude Code binary.

Start here

We split Claude Code’s architecture into eight chapters and walk through them like a tour—one main idea per chapter, with diagrams and analogies instead of dumping raw code on you.

Ready? Let’s start with the big question—what is the core idea behind Claude Code?

What is this? ​

Claude Code in 30 seconds ​

What this site covers ​

What you do not need ​