Claude Code’s source code appears to have leaked because an early npm release was shipped with source-map data still attached. A developer inspecting the bundled cli.mjs file noticed --enable-source-maps and then found a huge sourceMappingURL block at the bottom, which suggested the package still contained enough mapping data to reconstruct the original source. Anthropic later removed the source map from newer updates, but by then the earlier package had already been downloaded and inspected, so the code could still be recovered from what was already published.

Claude Code CLI is a sophisticated terminal application that provides an interactive interface for developers to collaborate with Claude (Anthropic's AI assistant) directly from their terminal. It combines the power of large language models with comprehensive file system operations, tool calling, and extensible architecture.

• Interactive AI Chat - Natural language coding assistance with real-time streaming responses
• File Operations - Read, edit, write, search, and analyze files with AI assistance
• Bash Execution - Execute shell commands with safety controls and sandboxing
• Web Integration - Search and fetch web content directly from the CLI
• Agent Swarms - Spawn sub-agents for parallel task execution
• Task Management - Track and manage background tasks and operations

• Multiple Execution Modes

  • Interactive REPL mode for conversational coding
  • Headless mode (-p/--print) for scripting and CI/CD pipelines
  • Remote session support via SSH and direct connections

• MCP (Model Context Protocol)

  • Connect to external tool servers
  • Dynamic tool discovery and execution
  • Enterprise-grade security with allowlist/denylist policies

• Context Management

  • Automatic context compaction for long conversations
  • Session persistence and resume capability
  • Project-specific memory and context

• Developer Tools

  • Git integration (commit, diff, branch management)
  • LSP (Language Server Protocol) support
  • Voice mode for speech-to-text input
  • Chrome/IDE integration

• Bun runtime (latest stable version recommended)
• Git (for repository operations)

# Install globally via npm
npm install -g @anthropic-ai/claude-code

# Or install via Bun
bun install -g @anthropic-ai/claude-code

# Or use the native installer (macOS/Linux)
curl -fsSL https://claude.ai/install.sh | sh

# Run the setup wizard
claude

# Or initialize with a specific directory
claude /path/to/your/project

# Authenticate with your Anthropic account
claude login

# Start interactive mode
claude

# Run in headless mode with a prompt
claude -p "Explain this codebase"

# Execute a command and exit
claude -p "Fix the bug in src/utils.ts" --allowedTools BashTool,FileEditTool

# Resume a previous session
claude --resume

Type / in the REPL to see all available commands. Here are the key ones:

Claude Code comes with 40+ built-in tools for file operations, execution, and integration:

• FileReadTool - Read files, images, PDFs with smart pagination
• FileEditTool - Edit files with sed-like functionality
• FileWriteTool - Create or overwrite files
• GlobTool - Find files using glob patterns
• GrepTool - Search file contents with regex
• NotebookEditTool - Edit Jupyter notebooks

• BashTool - Execute shell commands with sandboxing
• PowerShellTool - Windows PowerShell execution

• WebFetchTool - Fetch web pages content
• WebSearchTool - Search the web

• AgentTool - Spawn sub-agents for parallel work
• TaskCreateTool/TaskStopTool/TaskListTool - Background task management

• MCPTool - Execute tools from MCP servers
• ListMcpResourcesTool/ReadMcpResourceTool - MCP resource management

{
  "theme": "dark",
  "autoCompactEnabled": true,
  "editorMode": "vim",
  "verbose": false,
  "mcpServers": {
    "my-server": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/path"]
    }
  }
}

{
  "allowedTools": ["BashTool", "FileEditTool", "FileReadTool"],
  "mcpServers": {
    "project-server": {
      "type": "sse",
      "url": "https://api.example.com/mcp"
    }
  }
}

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "."]
    },
    "github": {
      "type": "sse",
      "url": "https://api.github.com/mcp",
      "oauth": {
        "clientId": "your-client-id"
      }
    }
  }
}

# Review the current PR
/review

# Security-focused review
/security-review

# Deep bug-finding review
/ultrareview

# Read a file with specific range
Please read src/main.ts lines 50-100

# Edit a file
Please update the config in package.json to add a new script

# Search across files
Find all TODO comments in the codebase

# Stage and commit changes
/commit

# Commit, push, and open PR
/commit-push-pr

# Show diff
/diff

# Create a background task
Please create a task to run the test suite in background

# List tasks
/tasks

# Stop a task
Please stop the test task

# Add an MCP server
/mcp add filesystem npx -y @modelcontextprotocol/server-filesystem .

# Use MCP tools
Please use the filesystem server to list all TypeScript files

User Input → REPL.tsx → QueryEngine → Claude API → Tool Execution → Response

• main.tsx - CLI entry point and argument parsing
• entrypoints/init.ts - System initialization and configuration
• screens/REPL.tsx - Interactive terminal UI
• QueryEngine.ts - Message submission and query coordination
• services/tools/ - Tool execution engine with concurrency control
• services/mcp/ - MCP client and server management