Tetrad

Tetrad

Quadruple Consensus MCP Server for Claude Code

Tetrad is a high-performance MCP (Model Context Protocol) server written in Rust that orchestrates three AI-powered CLI code evaluation tools (Codex, Gemini CLI, Qwen) to validate all code produced by Claude Code.

The system implements a quadruple consensus protocol where no code or plan is accepted without approval from four intelligences: the three external evaluators + Claude Code itself.

Features

• Quadruple Consensus: 4 AI models must agree to approve code
• ReasoningBank: Continuous learning system with RETRIEVE→JUDGE→DISTILL→CONSOLIDATE cycle
• High Performance: Written in Rust with parallel execution via Tokio
• MCP Server: JSON-RPC 2.0 server over stdio for Claude Code integration
• Full CLI: Intuitive commands (init, serve, status, doctor, config, etc.)
• LRU Cache: Result caching with configurable TTL
• Hook System: Pre/post evaluation callbacks for customization
• Extensible: Plugin system for custom executors
• Cross-session: SQLite persistence for patterns and history

Quick Start

1. Install Tetrad

# Via npm (recommended - works seamlessly with Claude Code)

npm install -g @samoradc/tetrad

Or via cargo (requires additional setup)

cargo install tetrad sudo cp ~/.cargo/bin/tetrad /usr/local/bin/

1.1 Initialize in Your Project (Optional)

npx @samoradc/tetrad init

This will:

• Create tetrad.toml configuration file
• Create .tetrad/ directory for the database
• Add .tetrad/ to your .gitignore

2. Install and Configure External CLI Tools

Tetrad requires at least one of the following AI CLI tools. Good news: you don't need separate API keys if you have existing subscriptions!

Codex CLI (OpenAI)

npm install -g @openai/codex

Authentication options:

# Option 1: Login with your ChatGPT subscription (recommended)

codex login

Opens browser for OAuth - follow the prompts

Option 2: Use API key

export OPENAI_API_KEY="your-openai-key"

Note: For headless/remote servers, use codex login --device-auth and follow the device code flow.

📖 Codex CLI Authentication Docs

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Gemini CLI (Google)

npm install -g @google/gemini-cli

Authentication options:

# Option 1: Login with Google account (recommended)

gemini auth login

Opens browser for OAuth - follow the prompts

Option 2: Use API key from Google AI Studio

export GEMINI_API_KEY="your-gemini-key"

Free Tier: With a personal Google account, you get access to Gemini 2.5 Pro with 1M token context window at no cost!

📖 Gemini CLI Authentication Docs

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Qwen CLI (Alibaba)

npm install -g qwen-code

Authentication options:

# Get your API key from DashScope console

export DASHSCOPE_API_KEY="your-dashscope-key"

For international users (outside China)

export OPENAI_BASE_URL="https://dashscope-intl.aliyuncs.com/compatible-mode/v1"

Regional Endpoints:

- Singapore: dashscope-intl.aliyuncs.com

- Virginia: dashscope-us.aliyuncs.com

- Beijing: dashscope.aliyuncs.com

📖 Qwen API Docs

3. Verify Installation

# Check Tetrad version

tetrad version

Check CLI availability

tetrad status

Diagnose any issues

tetrad doctor

4. Add to Claude Code CLI

# Add Tetrad as MCP server (all projects)

claude mcp add --scope user tetrad -- npx @samoradc/tetrad serve

Verify it's configured

claude mcp list

Alternative installation methods

# Current project only

claude mcp add tetrad -- npx @samoradc/tetrad serve

If installed via cargo

claude mcp add --scope user tetrad -- tetrad serve

Note: Tetrad is published on the MCP Registry for discoverability and documentation.

5. Alternative: Manual Configuration

Create or edit .mcp.json in your project root:

{

"mcpServers": { "tetrad": { "type": "stdio", "command": "npx", "args": ["@samoradc/tetrad", "serve"], "env": { "OPENAI_API_KEY": "${OPENAI_API_KEY}", "GOOGLE_API_KEY": "${GOOGLE_API_KEY}", "DASHSCOPE_API_KEY": "${DASHSCOPE_API_KEY}" } } } }

Or for global user configuration in ~/.claude.json (mcpServers section):

{

"mcpServers": { "tetrad": { "type": "stdio", "command": "npx", "args": ["@samoradc/tetrad", "serve"] } } }

How It Works

When you ask Claude Code to write code, Tetrad automatically validates it:

You: "Create a function in Rust that calculates the average of a vector"

Claude Code:

1. Writes the code
2. Calls tetrad_review_code automatically
3. Tetrad sends to Codex, Gemini and Qwen for evaluation
4. Returns consolidated consensus from all 3 evaluators

Tetrad Response: ┌─────────────────────────────────────────────┐ │ DECISION: PASS ✓ │ │ Score: 92/100 │ │ Consensus: Yes (3/3 approved) │ │ │ │ Votes: │ │ • Codex: Pass (95) │ │ • Gemini: Pass (90) │ │ • Qwen: Pass (92) │ │ │ │ Suggestions: │ │ - Consider handling empty vector case │ └─────────────────────────────────────────────┘

Claude Code: Saves the approved code

When Issues Are Found:

Tetrad Response:

┌─────────────────────────────────────────────┐ │ DECISION: BLOCK ✗ │ │ Score: 26/100 │ │ Consensus: Yes (3/3 rejected) │ │ │ │ Votes: │ │ • Codex: Fail (30) - division by zero │ │ • Gemini: Fail (25) - no error handling │ │ • Qwen: Fail (25) - unsafe operation │ │ │ │ Issues: │ │ - Division by zero not handled │ │ - Missing input validation │ │ - No Result/Option return type │ └─────────────────────────────────────────────┘

Claude Code: Fixes the code and resubmits

CLI Commands

tetrad - Quadruple Consensus CLI for Claude Code

COMMANDS: init Initialize configuration in current directory serve Start the MCP server (used by Claude Code) status Show CLI status (codex, gemini, qwen) config Configure options interactively doctor Diagnose configuration issues version Show version evaluate Evaluate code manually (without MCP) history Show evaluation history from ReasoningBank export Export patterns from ReasoningBank import Import patterns into ReasoningBank

OPTIONS: -c, --config Configuration file (default: tetrad.toml) -v, --verbose Verbose mode -q, --quiet Quiet mode -h, --help Show help

MCP Tools

When running as MCP server, Tetrad exposes 6 tools:

Workflow Example

1. Claude Code generates plan → tetrad_review_plan → Feedback

1. Claude Code implements → tetrad_review_code → Feedback
2. Claude Code adjusts → tetrad_confirm → Confirmation
3. Claude Code finalizes → tetrad_final_check → Certificate

Architecture

Claude Code → MCP Protocol (stdio) → Tetrad Server (Rust)

│ ┌─────────────────────┼─────────────────────┐ ▼ ▼ ▼ Codex CLI Gemini CLI Qwen CLI (syntax) (architecture) (logic) │ │ │ └─────────────────────┼─────────────────────┘ ▼ Consensus Engine │ ┌─────────────┴─────────────┐ ▼ ▼ LRU Cache ReasoningBank (results) (SQLite) RETRIEVE→JUDGE→DISTILL→CONSOLIDATE

Executor Specializations

Consensus Rules

ReasoningBank

The ReasoningBank is a continuous learning system that stores and consolidates code patterns:

Learning Cycle

RETRIEVE → JUDGE → DISTILL → CONSOLIDATE

│ │ │ │ │ │ │ └─ Merge similar patterns │ │ └─ Extract new patterns │ └─ Evaluate code with context └─ Search for relevant patterns

Pattern Types

• AntiPattern: Patte