claude-code

Claude Code — Leaked Source (2026-03-31)

On March 31, 2026, the full source code of Anthropic's Claude Code CLI was leaked via a .map file exposed in their npm registry.

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How It Leaked

Chaofan Shou (@Fried_rice) discovered the leak and posted it publicly:

"Claude code source code has been leaked via a map file in their npm registry!"

— @Fried_rice, March 31, 2026

The source map file in the published npm package contained a reference to the full, unobfuscated TypeScript source, which was downloadable as a zip archive from Anthropic's R2 storage bucket.

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Quick Setup

Prerequisites

• Bun v1.3+ (the project's runtime)
• Node.js v18+ (for npm package installation)
• An Anthropic API key (set as ANTHROPIC_API_KEY environment variable)

Install & Run

# 1. Install Bun (if not already installed)
curl -fsSL https://bun.sh/install | bash
source ~/.bash_profile  # or restart your terminal

# 2. Install dependencies
npm install --legacy-peer-deps

# 3. Run Claude Code
bun run start

# Or with arguments:
bun run start -- --help
bun run start -- --version
bun run start -- -p "Hello Claude"

Available Scripts

Script Description bun run start Run Claude Code CLI bun run dev Run with hot-reloading (--watch) bun run build Bundle for production bun run typecheck Run TypeScript type checking

Environment Variables

Variable Description ANTHROPIC_API_KEY Your Anthropic API key (required to use Claude) FEATURE_FLAGS Comma-separated list of feature flags to enable (e.g., KAIROS,VOICE_MODE)

Notes

• Some modules from the original source were not included in the leak (Anthropic-internal @ant/* packages, some tools). These have been replaced with stubs that export no-ops.
• The bun:bundle feature flag system is shimmed via a Bun plugin at plugins/bunBundleDev.ts. All flags default to false unless enabled via FEATURE_FLAGS.
• The MACRO.* build-time constants are defined in bunfig.toml and injected by Bun's --define system.

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Overview

Claude Code is Anthropic's official CLI tool that lets you interact with Claude directly from the terminal to perform software engineering tasks — editing files, running commands, searching codebases, managing git workflows, and more.

This repository contains the leaked src/ directory.

• Leaked on: 2026-03-31
• Language: TypeScript
• Runtime: Bun
• Terminal UI: React + Ink (React for CLI)
• Scale: ~1,900 files, 512,000+ lines of code

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Directory Structure

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Core Architecture

1. Tool System (src/tools/)

Every tool Claude Code can invoke is implemented as a self-contained module. Each tool defines its input schema, permission model, and execution logic.

Tool Description BashTool Shell command execution FileReadTool File reading (images, PDFs, notebooks) FileWriteTool File creation / overwrite FileEditTool Partial file modification (string replacement) GlobTool File pattern matching search GrepTool ripgrep-based content search WebFetchTool Fetch URL content WebSearchTool Web search AgentTool Sub-agent spawning SkillTool Skill execution MCPTool MCP server tool invocation LSPTool Language Server Protocol integration NotebookEditTool Jupyter notebook editing TaskCreateTool / TaskUpdateTool Task creation and management SendMessageTool Inter-agent messaging TeamCreateTool / TeamDeleteTool Team agent management EnterPlanModeTool / ExitPlanModeTool Plan mode toggle EnterWorktreeTool / ExitWorktreeTool Git worktree isolation ToolSearchTool Deferred tool discovery CronCreateTool Scheduled trigger creation RemoteTriggerTool Remote trigger SleepTool Proactive mode wait SyntheticOutputTool Structured output generation

2. Command System (src/commands/)

User-facing slash commands invoked with / prefix.

Command Description /commit Create a git commit /review Code review /compact Context compression /mcp MCP server management /config Settings management /doctor Environment diagnostics /login / /logout Authentication /memory Persistent memory management /skills Skill management /tasks Task management /vim Vim mode toggle /diff View changes /cost Check usage cost /theme Change theme /context Context visualization /pr_comments View PR comments /resume Restore previous session /share Share session /desktop Desktop app handoff /mobile Mobile app handoff

3. Service Layer (src/services/)

Service Description api/ Anthropic API client, file API, bootstrap mcp/ Model Context Protocol server connection and management oauth/ OAuth 2.0 authentication flow lsp/ Language Server Protocol manager analytics/ GrowthBook-based feature flags and analytics plugins/ Plugin loader compact/ Conversation context compression policyLimits/ Organization policy limits remoteManagedSettings/ Remote managed settings extractMemories/ Automatic memory extraction tokenEstimation.ts Token count estimation teamMemorySync/ Team memory synchronization

4. Bridge System (src/bridge/)

A bidirectional communication layer connecting IDE extensions (VS Code, JetBrains) with the Claude Code CLI.

• bridgeMain.ts — Bridge main loop
• bridgeMessaging.ts — Message protocol
• bridgePermissionCallbacks.ts — Permission callbacks
• replBridge.ts — REPL session bridge
• jwtUtils.ts — JWT-based authentication
• sessionRunner.ts — Session execution management

5. Permission System (src/hooks/toolPermission/)

Checks permissions on every tool invocation. Either prompts the user for approval/denial or automatically resolves based on the configured permission mode (default, plan, bypassPermissions, auto, etc.).

6. Feature Flags

Dead code elimination via Bun's bun:bundle feature flags:

import { feature } from 'bun:bundle'

// Inactive code is completely stripped at build time
const voiceCommand = feature('VOICE_MODE')
  ? require('./commands/voice/index.js').default
  : null

Notable flags: PROACTIVE, KAIROS, BRIDGE_MODE, DAEMON, VOICE_MODE, AGENT_TRIGGERS, MONITOR_TOOL

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Key Files in Detail

QueryEngine.ts (~46K lines)

The core engine for LLM API calls. Handles streaming responses, tool-call loops, thinking mode, retry logic, and token counting.

Tool.ts (~29K lines)

Defines base types and interfaces for all tools — input schemas, permission models, and progress state types.

commands.ts (~25K lines)

Manages registration and execution of all slash commands. Uses conditional imports to load different command sets per environment.

main.tsx

Commander.js-based CLI parser + React/Ink renderer initialization. At startup, parallelizes MDM settings, keychain prefetch, and GrowthBook initialization for faster boot.

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Tech Stack

Category Technology Runtime Bun Language TypeScript (strict) Terminal UI React + Ink CLI Parsing Commander.js (extra-typings) Schema Validation Zod v4 Code Search ripgrep (via GrepTool) Protocols MCP SDK, LSP API Anthropic SDK Telemetry OpenTelemetry + gRPC Feature Flags GrowthBook Auth OAuth 2.0, JWT, macOS Keychain

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Notable Design Patterns

Parallel Prefetch

Startup time is optimized by prefetching MDM settings, keychain reads, and API preconnect in parallel — before heavy module evaluation begins.

// main.tsx — fired as side-effects before other imports
startMdmRawRead()
startKeychainPrefetch()

Lazy Loading

Heavy modules (OpenTelemetry ~400KB, gRPC ~700KB) are deferred via dynamic import() until actually needed.

Agent Swarms

Sub-agents are spawned via AgentTool, with coordinator/ handling multi-agent orchestration. TeamCreateTool enables team-level parallel work.

Skill System

Reusable workflows defined in skills/ and executed through SkillTool. Users can add custom skills.

Plugin Architecture

Built-in and third-party plugins are loaded through the plugins/ subsystem.

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Disclaimer

This repository archives source code that was leaked from Anthropic's npm registry on 2026-03-31. All original source code is the property of Anthropic.