Claude Code — Source Code

The full source code of Anthropic's Claude Code CLI, made public on March 31, 2026

The original unmodified source is preserved in the backup branch.

Table of Contents

• How It Became Public
• What Is Claude Code?
• Documentation
• Explore with MCP Server
• Directory Structure
• Architecture
  • Tool System
  • Command System
  • Service Layer
  • Bridge System
  • Permission System
  • Feature Flags
• Key Files
• Tech Stack
• Design Patterns
• GitPretty Setup
• Contributing
• Disclaimer

How It Became Public

Chaofan Shou (@Fried_rice) discovered that the published npm package for Claude Code included a .map file referencing the full, unobfuscated TypeScript source — accessible as a zip from Anthropic's R2 storage bucket.

An Anthropic employee subsequently made the source available in the public domain on March 31, 2026.

What Is Claude Code?

Claude Code is Anthropic's official CLI tool for interacting with Claude directly from the terminal — editing files, running commands, searching codebases, managing git workflows, and more. This repository contains the src/ directory.

| | | |---|---| | Published | 2026-03-31 | | Language | TypeScript (strict) | | Runtime | Bun | | Terminal UI | React + Ink | | Scale | ~1,900 files · 512,000+ lines of code |

📚 Documentation

For in-depth guides, see the docs/ directory:

| Guide | Description | |-------|-------------| | Architecture | Core pipeline, startup sequence, state management, rendering, data flow | | Tools Reference | Complete catalog of all ~40 agent tools with categories and permission model | | Commands Reference | All ~85 slash commands organized by category | | Subsystems Guide | Deep dives into Bridge, MCP, Permissions, Plugins, Skills, Tasks, Memory, Voice | | Exploration Guide | How to navigate the codebase — study paths, grep patterns, key files |

Also see: CONTRIBUTING.md · MCP Server README

🔍 Explore with MCP Server

This repo ships an MCP server that lets any MCP-compatible client (Claude Code, Claude Desktop, VS Code Copilot, Cursor) explore the full source interactively.

Install from npm

The MCP server is published as claude-code-explorer-mcp on npm — no need to clone the repo:

# Claude Code
claude mcp add claude-code-explorer -- npx -y claude-code-explorer-mcp

One-liner setup (from source)

git clone https://github.com/nirholas/claude-code.git ~/claude-code \
  && cd ~/claude-code/mcp-server \
  && npm install && npm run build \
  && claude mcp add claude-code-explorer -- node ~/claude-code/mcp-server/dist/index.js

# 1. Clone the repo
git clone https://github.com/nirholas/claude-code.git
cd claude-code/mcp-server

# 2. Install & build
npm install && npm run build

# 3. Register with Claude Code
claude mcp add claude-code-explorer -- node /absolute/path/to/claude-code/mcp-server/dist/index.js

Replace /absolute/path/to/claude-code with your actual clone path.

VS Code — add to .vscode/mcp.json:

{
  "servers": {
    "claude-code-explorer": {
      "type": "stdio",
      "command": "node",
      "args": ["${workspaceFolder}/mcp-server/dist/index.js"],
      "env": { "CLAUDE_CODE_SRC_ROOT": "${workspaceFolder}/src" }
    }
  }
}

Claude Desktop — add to your config file:

{
  "mcpServers": {
    "claude-code-explorer": {
      "command": "node",
      "args": ["/absolute/path/to/claude-code/mcp-server/dist/index.js"],
      "env": { "CLAUDE_CODE_SRC_ROOT": "/absolute/path/to/claude-code/src" }
    }
  }
}

Cursor — add to ~/.cursor/mcp.json (same format as Claude Desktop).

Available tools & prompts

| Tool | Description | |------|-------------| | list_tools | List all ~40 agent tools with source files | | list_commands | List all ~50 slash commands with source files | | get_tool_source | Read full source of any tool (e.g. BashTool, FileEditTool) | | get_command_source | Read source of any slash command (e.g. review, mcp) | | read_source_file | Read any file from src/ by path | | search_source | Grep across the entire source tree | | list_directory | Browse src/ directories | | get_architecture | High-level architecture overview |

| Prompt | Description | |--------|-------------| | explain_tool | Deep-dive into how a specific tool works | | explain_command | Understand a slash command's implementation | | architecture_overview | Guided tour of the full architecture | | how_does_it_work | Explain any subsystem (permissions, MCP, bridge, etc.) | | compare_tools | Side-by-side comparison of two tools |

Try asking: "How does the BashTool work?" · "Search for where permissions are checked" · "Show me the /review command source"

Custom source path / Remove

# Custom source location
claude mcp add claude-code-explorer -e CLAUDE_CODE_SRC_ROOT=/path/to/src -- node /path/to/mcp-server/dist/index.js

# Remove
claude mcp remove claude-code-explorer

Directory Structure

src/
├── main.tsx                 # Entrypoint — Commander.js CLI parser + React/Ink renderer
├── QueryEngine.ts           # Core LLM API caller (~46K lines)
├── Tool.ts                  # Tool type definitions (~29K lines)
├── commands.ts              # Command registry (~25K lines)
├── tools.ts                 # Tool registry
├── context.ts               # System/user context collection
├── cost-tracker.ts          # Token cost tracking
│
├── tools/                   # Agent tool implementations (~40)
├── commands/                # Slash command implementations (~50)
├── components/              # Ink UI components (~140)
├── services/                # External service integrations
├── hooks/                   # React hooks (incl. permission checks)
├── types/                   # TypeScript type definitions
├── utils/                   # Utility functions
├── screens/                 # Full-screen UIs (Doctor, REPL, Resume)
│
├── bridge/                  # IDE integration (VS Code, JetBrains)
├── coordinator/             # Multi-agent orchestration
├── plugins/                 # Plugin system
├── skills/                  # Skill system
├── server/                  # Server mode
├── remote/                  # Remote sessions
├── memdir/                  # Persistent memory directory
├── tasks/                   # Task management
├── state/                   # State management
│
├── voice/                   # Voice input
├── vim/                     # Vim mode
├── keybindings/             # Keybinding configuration
├── schemas/                 # Config schemas (Zod)
├── migrations/              # Config migrations
├── entrypoints/             # Initialization logic
├── query/                   # Query pipeline
├── ink/                     # Ink renderer wrapper
├── buddy/                   # Companion sprite (Easter egg 🐣)
├── native-ts/               # Native TypeScript utils
├── outputStyles/            # Output styling
└── upstreamproxy/           # Proxy configuration

Architecture

1. Tool System

src/tools/ — Every tool Claude can invoke is a self-contained module with its own input schema, permission model, and execution logic.

| Tool | Description | |---|---| | File I/O | | | FileReadTool | Read files (images, PDFs, notebooks) | | FileWriteTool | Create / overwrite files | | FileEditTool | Partial modification (string replacement) | | NotebookEditTool | Jupyter notebook editing | | Search | | | GlobTool | File pattern matching | | GrepTool | ripgrep-based content search | | WebSearchTool | Web search | | WebFetchTool | Fetch URL content | | Execution | | | BashTool | Shell command execution | | SkillTool | Skill execution | | MCPTool | MCP server tool invocation | | LSPTool | Language Server Protocol integration | | Agents & Teams | | | AgentTool | Sub-agent spawning | | SendMessageTool | Inter-agent messaging | | TeamCreateTool / TeamDeleteTool | Team management | | TaskCreateTool / TaskUpdateTool | Task management | | Mode & State | | | EnterPlanModeTool / ExitPlanModeTool | Plan mode toggle | | EnterWorktreeTool / ExitWorktreeTool | Git worktree isolation | | `ToolSearchT