Claude Code Anatomy

How Claude Code actually works, from the decompiled source.

Why This Exists

Claude Code ships as an opaque binary. You can't read how it picks tools, gates permissions, or coordinates agents. So we decompiled it from npm source maps and documented the internals across 4,756 TypeScript files. Key sections include framework comparisons (ADK, OpenAI Agents SDK, LangChain, LangGraph) so the patterns are portable to your own agent architecture.

Scope

Some areas of the recovered tree are feature-gated, stubbed, or only partially present. When a subsystem could not be verified directly from source, this site intentionally avoids speculating beyond the observable implementation.

How to Read This Site

Sequential — Read Core Architecture in order: Agent Loop → Sub-Agents → Headless Query Engine & SDK Protocol → Tool System → Task Management → Prompt, Memory & Context → State & Sessions. This traces how the local and headless runtimes fit together.

By topic — Jump to any section. Extensions and Security are self-contained. Runtime & Infrastructure covers startup, rendering, API internals, and remote session architecture.

As a reference — The Appendix has the full directory map, all 90+ feature flags, the command catalog, complete tool definitions, and a glossary.

Architecture at a Glance

👤

User Input

📥

cli.tsx - Bootstrap

⚙️

main.tsx - Initialization

🖥️

REPL Screen - React/Ink

⌨️

Prompt Input

💬

Message Display

❓

Slash Command?

📋

Yes: Command System

⚙️

No: Query Engine

Query Engine Pipeline

📝

System Prompt Assembly

📡

API Call - Anthropic/Bedrock/Vertex

📡

Streaming Response

❓

Tool Use?

Yes: Tool Pipeline

🔒

Permission Check

🔧

Tool Execution

📤

Tool Result → back to API

✅

No: Render Response

Extensions

MCP Servers

Plugins

Skills

State

Zustand Store

React Contexts

CLAUDE.md Layers

Source Recovery

This analysis is based on source code recovered from the @anthropic-ai/claude-code v2.1.88 npm package. The published bundle includes a source map (cli.js.map) containing all 4,756 original TypeScript source files with full sourcesContent, enabling lossless restoration:

# Extract sources from the source map
node -e "
const fs = require('fs'), path = require('path');
const map = JSON.parse(fs.readFileSync('package/cli.js.map', 'utf8'));
for (let i = 0; i < map.sources.length; i++) {
  const content = map.sourcesContent[i];
  if (!content) continue;
  let relPath = map.sources[i];
  while (relPath.startsWith('../')) relPath = relPath.slice(3);
  const outPath = path.join('./claude-code-source', relPath);
  fs.mkdirSync(path.dirname(outPath), { recursive: true });
  fs.writeFileSync(outPath, content);
}
"

By the Numbers

Metric	Value
Source files	4,756
Core source (src/ + vendor/)	1,906 files
Built-in tools	45+
Slash commands	100+
Feature flags	90+
npm dependencies	489 packages
Build output	~22 MB
Version analyzed	2.1.88

Technology Stack

	Technology	Role
	TypeScript 6.0	Language
	React 19 + Ink 6	Terminal UI framework
	Bun	Build tool
	Custom store	State management
	Zod	Schema validation
	Commander	Argument parsing
	Anthropic SDK	API client
	MCP SDK	Model Context Protocol
	OpenTelemetry	Observability