Open Claude Code

Open Source Claude Code CLI — Reverse Engineered & Rebuilt

!Verified release pipeline: detect, validate, test, publish

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

Verified nightly releases: Detection, source validation, tests, AI analysis and npm publication run automatically. Capability proposals require review before implementation. See the release workflow and ADR-004.

⚡ 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?"

🧠 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.

1,008 unit tests plus installed-package behavioral checks. Full upstream parity is not established.

📦 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"

🖥️ 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"

🔧 Interactive Commands

40 slash commands available in REPL mode:

| Command | Description | |---------|-------------| | /help | Show all commands | | /model | 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 | 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 |

🔨 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 |

⚙️ 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

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

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

🔐 Multi-Provider Support

Adapters exist for Anthropic, OpenAI-compatible endpoints and Google. Installed-package E2E covers Anthropic and OpenAI-compatible tool roundtrips; Google is not covered by that gate. Bedrock and Vertex remain stubs.

# Anthropic (default)
ANTHROPIC_API_KEY=... occ "hello"
OpenAI
OPENAI_API_KEY=... occ -m gpt-4o "hello"
Google
GOOGLE_API_KEY=... occ -m gemini-2.5-flash "hello"

🔗 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.

🔍 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 →

⚖️ 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.

📚 Related

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

Verified release automation

!Installed CLI end to end verification

Runs daily at 03:00 UTC. Unchanged upstream versions are explicitly reported as no-op runs.

Publication requires unit and regression tests, a dependency audit, validated source recovery, successful AI analysis, clean package installation tests, and a live provider Read tool roundtrip against a fresh random fixture. The exact tested tarball is published to npm, its SHA-512 integrity verified, and the registry version installed and exercised again.

Only then does the upstream checkpoint advance. Failed gates stop publication and create an investigation issue. GitHub releases attach the package, source commit receipt and analysis. Nightly versions use the npm nightly tag. Stable releases require the manually selected latest channel.

Required repository secrets: AI_API_KEY (OpenRouter) and NPM_TOKEN with publishing permission. GITHUB_TOKEN is supplied by GitHub Actions. ruOS bindings provision credentials without printing their values.

gh workflow run nightly.yml -f force_release=true -f channel=nightly
npm install @ruvnet/open-claude-code@nightly

Structural changes produce review proposals, not implemented features. Concrete behavioral specifications and new tests are required before implementing them. Full upstream parity is not established.

See release integrity ADR.

📄 License

MIT