Open Claude Code

Open Source Claude Code CLI — Reverse Engineered & Rebuilt

A fully functional open source implementation of Anthropic's Claude Code CLI,
built from decompiled source intelligence using ruDevolution.

Automated Nightly Releases — Open Claude Code automatically detects new Claude Code releases, runs 903+ tests to verify zero regressions, and publishes verified builds with AI-powered discovery analysis. See Releases | ADR-001 | pi.ruv.io

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⚡ Quick Start

# Run instantly (no install)
npx @ruvnet/open-claude-code "explain this codebase"

# Or install globally
npm install -g @ruvnet/open-claude-code
occ "hello"

# Interactive mode
occ

Requires: ANTHROPIC_API_KEY environment variable set.

export ANTHROPIC_API_KEY=sk-ant-...
npx @ruvnet/open-claude-code "what files are in this directory?"

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🧠 What Is This?

Open Claude Code is a ground-up open source rebuild of Anthropic's Claude Code CLI, informed by ruDevolution's AI-powered decompilation of the published npm package.

It's not a copy — it's a clean-room implementation that mirrors the actual Claude Code architecture: async generator agent loop, 25 tools, 4 MCP transports, 6 permission modes, hooks, settings chain, sessions, and more.

1,581 tests. 61 files. 8,314 lines. 100% functional.

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📦 Installation

npx (no install needed)

npx @ruvnet/open-claude-code "your prompt here"

Global install

npm install -g @ruvnet/open-claude-code
occ "your prompt here"

From source

git clone https://github.com/ruvnet/open-claude-code.git
cd open-claude-code/v2
export ANTHROPIC_API_KEY=sk-ant-...
node src/index.mjs "hello"

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🖥️ Usage

One-shot mode

occ "explain the auth module"
occ "fix the bug in server.js"
occ "create a REST API for user management"
occ "find all TODO comments in this project"

Interactive REPL

occ
# > explain this codebase
# > /help
# > /tools
# > /model claude-opus-4-6
# > refactor the database layer
# > /cost
# > /exit

CLI Options

occ [options] [prompt]

Options:
  -m, --model <model>          Model to use (default: claude-sonnet-4-6)
  -p, --print                  Print mode (non-interactive, output only)
  --permission-mode <mode>     Permission mode: default, auto, plan, acceptEdits, 
                               bypassPermissions, dontAsk
  --system-prompt <text>       Override system prompt
  --add-dir <path>             Additional CLAUDE.md directory
  --max-turns <n>              Maximum conversation turns
  --allowedTools <tools>       Comma-separated allowed tools
  --disallowedTools <tools>    Comma-separated denied tools
  --output-format <fmt>        Output: text, json, stream-json
  -v, --verbose                Verbose output
  -d, --debug                  Debug mode
  --version                    Show version
  -h, --help                   Show help

Examples

# Use a different model
occ -m claude-opus-4-6 "design a database schema for a blog"

# Print mode (for piping)
occ -p "list all functions in src/" > functions.txt

# Plan mode (read-only, no edits)
occ --permission-mode plan "review the security of auth.js"

# Restrict tools
occ --allowedTools "Read,Glob,Grep" "find all API endpoints"

# With custom system prompt
occ --system-prompt "You are a senior Go developer" "review main.go"

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🔧 Interactive Commands

40 slash commands available in REPL mode:

Command	Description
/help	Show all commands
/model <name>	Switch model mid-conversation
/tools	List available tools
/tokens	Show current token usage
/cost	Show session cost estimate
/compact	Compact context window
/undo	Undo last file edit
/clear	Clear conversation history
/doctor	Check API connectivity + health
/fast	Toggle fast mode (Haiku)
/effort <level>	Set effort: low, medium, high, max
/resume [id]	Resume a previous session
/sessions	List saved sessions
/agents	List custom agents
/skills	List available skills
/hooks	Show active hooks
/config	Show current settings
/permissions	Show permission mode
/mcp	Show MCP server status
/memory	Show memory usage
/exit	Exit

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🔨 Tools

25 built-in tools matching Claude Code's tool system:

Tool	Description
Bash	Execute shell commands (sandboxed)
Read	Read files with line numbers
Edit	Replace strings in files
Write	Create/overwrite files
Glob	Find files by pattern
Grep	Search file contents (regex)
LS	List directory contents
Agent	Spawn sub-agents
WebFetch	Fetch URL content
WebSearch	Web search
TodoWrite	Task management
NotebookEdit	Edit Jupyter notebooks
MultiEdit	Atomic multi-file edits
ToolSearch	Discover deferred tools
AskUser	Prompt user for input
Skill	Invoke a skill
SendMessage	Agent team messaging
CronCreate/Delete/List	Scheduled tasks
EnterWorktree/ExitWorktree	Git worktree isolation
RemoteTrigger	Remote execution
LSP	Language server protocol
ReadMcpResource	Read MCP resources

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⚙️ Configuration

Settings

Create .claude/settings.json in your project or ~/.claude/settings.json globally:

{
  "model": "claude-sonnet-4-6",
  "permissions": {
    "defaultMode": "auto"
  },
  "hooks": {
    "PreToolUse": [{
      "matcher": "Bash",
      "hooks": [{ "type": "command", "command": "echo 'Running bash...'" }]
    }]
  },
  "autoCompactEnabled": true,
  "alwaysThinkingEnabled": true
}

Settings are loaded from 4 sources (in priority order):

1. .claude/settings.local.json (local, gitignored)
2. .claude/settings.json (project, shared)
3. ~/.claude/settings.json (user global)
4. Managed policy (enterprise)

CLAUDE.md

Create a CLAUDE.md in your project root to customize behavior:

# Project Rules
- Always use TypeScript
- Follow TDD
- Keep files under 500 lines

CLAUDE.md files are loaded from: ~/.claude/CLAUDE.md → parent directories → project root → .claude/CLAUDE.md.

Custom Agents

Create .claude/agents/reviewer.md:

---
name: reviewer
description: Code review specialist
model: claude-sonnet-4-6
tools: [Read, Glob, Grep]
---

You are a thorough code reviewer. Check for bugs, security issues, and style.

Skills

Create .claude/skills/deploy/SKILL.md:

---
name: deploy
description: Deploy to production
---

1. Run tests: npm test
2. Build: npm run build
3. Deploy: ./scripts/deploy.sh

Invoke with /deploy in the REPL.

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🔐 Multi-Provider Support

Works with 5 AI providers:

# Anthropic (default)
ANTHROPIC_API_KEY=... occ "hello"

# OpenAI
OPENAI_API_KEY=... occ -m gpt-4o "hello"

# Google
GOOGLE_AI_API_KEY=... occ -m gemini-2.5-flash "hello"

# AWS Bedrock
AWS_ACCESS_KEY_ID=... AWS_SECRET_ACCESS_KEY=... occ -m bedrock/claude-sonnet "hello"

# Google Vertex
GOOGLE_APPLICATION_CREDENTIALS=... occ -m vertex/claude-sonnet "hello"

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🔗 MCP Integration

Connect to MCP servers for additional tools:

// .mcp.json
{
  "mcpServers": {
    "my-server": {
      "command": "npx",
      "args": ["-y", "my-mcp-server"],
      "env": { "API_KEY": "..." }
    }
  }
}

Supports 4 transports: stdio, SSE, Streamable HTTP, WebSocket.

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🔍 Background: The Claude Code Source Leak

On March 31, 2026, Anthropic accidentally shipped source maps in the Claude Code npm package, exposing the full TypeScript source. This project takes a different approach — we use ruDevolution to analyze the published npm package legally and rebuild from that intelligence.

What ruDevolution Found

Discovery	Evidence
🤖 Agent Teams	CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS
🌙 Auto Dream Mode	tengu_auto_dream_completed
🔮 claude-opus-4-6	Unreleased model ID
🔐 6 "amber" codenames	Internal feature gates
☁️ Cloud Code Runner	BYOC compute
📡 MCP Streamable HTTP	New transport

Download decompiled releases →

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⚖️ Legal

This is a clean-room implementation — no leaked source used. Architecture informed by analysis of the published npm package, legal under US DMCA §1201(f), EU Software Directive Art. 6, UK CDPA §50B.

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📚 Related

• ruDevolution — AI-Powered JavaScript Decompiler
• Decompiled Releases — Every Claude Code version
• v2 Architecture (ADR-001)
• Path to 100% (ADR-002)

Nightly Release Pipeline

Automated Nightly Verified Releases (ADR-001)

Open Claude Code includes an automated nightly CI/CD pipeline that:

1. Detects new Claude Code releases from npm registry (03:00 UTC daily)
2. Verifies compatibility with 903+ tests, npm audit, and smoke tests
3. Analyzes changes using Claude Sonnet 4.6 AI-powered discovery
4. Publishes verified releases with detailed notes — only if ALL gates pass

Cron 03:00 UTC → npm check → 903+ tests → npm audit → AI analysis → verified release

Manual trigger:

gh workflow run nightly.yml -f force_release=true

Required secrets:

• GITHUB_TOKEN — automatic
• ANTHROPIC_API_KEY — optional, for AI discovery analysis

See ADR-001 for full architecture.

rudevolution Integration

The rudevolution submodule provides AI-powered decompilation analysis of Claude Code releases, tracking 34,759+ functions with 95.7% name accuracy. Used by the nightly pipeline for change discovery.

📄 License

MIT