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

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.

2. Command System (src/commands/)​

User-facing slash commands invoked with / prefix.

3. Service Layer (src/services/)​

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

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.

Tech Stack​

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.

GitPretty Setup (Per-File Pretty Commits)​

If you want GitHub's file UI to show visually distinct commit messages per file, use the helper script in this repo:
bash ./gitpretty-apply.sh .
This will:

1. Clone gitpretty into ~/.gitpretty (first run only)
2. Make scripts executable
3. Run emoji-file-commits.sh against this repo

Optional: install auto-emoji hooks for future commits:
bash ./gitpretty-apply.sh . --hooks
After running, push as usual:
git push origin main

Use It in Claude Code (MCP Server)​

This repo includes an MCP server that lets you explore the Claude Code source directly from any Claude session. One command to set it up:

Quick Start​

# Clone the repo (if you haven't already)
git clone https://github.com/Atharvsinh-codez/claude-code.git
cd claude-code/mcp-server

# Install dependencies and build
npm install && npm run build

# Add to Claude Code (run from the repo root)
claude mcp add claude-code-explorer -- node /absolute/path/to/claude-code/mcp-server/dist/index.js
Replace /absolute/path/to/claude-code with the actual path where you cloned the repo.
Or as a single copy-paste block (clones, builds, and registers in one go):
git clone https://github.com/Atharvsinh-codez/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

What You Get​

Once added, Claude has access to these tools for exploring the codebase:

Plus prompts for guided exploration:

• 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

Example Usage​

After adding the MCP server, just ask Claude naturally:
"How does the BashTool work?" "Search for where permissions are checked" "Show me the /review command source" "Explain the MCP client integration"

Custom Source Path​

If your src/ directory is in a non-standard location, set the environment variable:
claude mcp add claude-code-explorer -e CLAUDE_CODE_SRC_ROOT=/path/to/src -- node /path/to/mcp-server/dist/index.js

Remove It​

claude mcp remove claude-code-explorer

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.