Codex MCP Server

Advanced MCP server wrapper for OpenAI Codex CLI v0.50.0+ that provides enterprise-grade conversational AI coding assistance with session management, intelligent model selection, and native resume functionality.

graph LR
    A[Claude Code] --> B[Codex MCP Server]

    B --> C[codex tool]
    B --> D[listSessions tool]
    B --> E[ping tool]
    B --> F[help tool]

    C --> G[Codex CLI v0.50.0+]
    C --> H[Session Storage]

    style A fill:#FF6B35
    style B fill:#4A90E2
    style C fill:#00D4AA
    style D fill:#00D4AA
    style E fill:#00D4AA
    style F fill:#00D4AA
    style G fill:#FFA500
    style H fill:#9B59B6

Prerequisites

OpenAI Codex CLI v0.50.0+ must be pre-installed and configured
- Install: npm i -g @openai/codex or brew install codex
- Setup: Run codex login --api-key "your-openai-api-key"
- ⚠️ Breaking Change: OPENAI_API_KEY environment variable is no longer supported
- ⚠️ Version Requirement: v0.50.0+ required (see Version Compatibility below)
Claude Code installed

Version Compatibility

This MCP server requires codex CLI v0.50.0 or later due to the following changes:

v0.50.0+: Introduced --skip-git-repo-check flag (now required)
v0.50.0+: Removed --reasoning-effort flag (no longer supported)

If you have an older version of codex CLI, you will need to upgrade:

npm update -g @openai/codex

For detailed version compatibility information, see docs/codex-cli-integration.md.

Installation

One-Click Installation

VS Code

VS Code Insiders

Cursor

Manual Installation

Claude Code

claude mcp add codex-cli -- npx -y codex-mcp-server

Claude Desktop

Add to your Claude Desktop configuration file:

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json

Windows: %APPDATA%/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "codex-cli": {
      "command": "npx",
      "args": ["-y", "codex-mcp-server"]
    }
  }
}

Usage in Claude Code

Once installed, Claude Code can use these tools:

`codex` - AI Coding Assistant

Ask Codex to analyze code, generate solutions, or provide coding assistance with optional session support for conversational context.

Basic Usage:

Use the codex tool to explain this function:
[paste your code here]

Advanced Usage:

# Model selection (defaults to gpt-5-codex)
Use codex with model "gpt-4" to analyze this complex algorithm

# Reasoning effort control
Use codex with reasoningEffort "high" for thorough code review

# Session with model preferences (using advanced GPT-5 Codex by default)
Use codex with sessionId "my-session" and model "gpt-4" to refactor this code

# Continue conversation (uses native codex resume)
Use codex with sessionId "my-session" to make it more efficient

# Reset session context
Use codex with sessionId "my-session" and resetSession true to start fresh analysis

Parameters:

prompt (required): Your coding question or request
sessionId (optional): Session ID for conversational context
resetSession (optional): Reset session history before processing
model (optional): Specify model to use (defaults to 'gpt-5-codex'). Options: 'gpt-5-codex', 'gpt-4', 'gpt-3.5-turbo'
reasoningEffort (optional): Control reasoning depth ('low', 'medium', 'high')

`listSessions` - Session Management

List all active conversation sessions with metadata including creation time, last access, and turn count.

Usage:

Use listSessions to see all active coding sessions

`ping` - Connection Test

Test if the MCP server is working properly.

`help` - Codex CLI Help

Get information about Codex CLI capabilities and commands.

Example Workflows

Code Analysis:

Please use the codex tool to review this TypeScript function and suggest improvements

Conversational Code Development:

# Start a session for complex refactoring
Use codex with sessionId "refactor-auth" to analyze this authentication system

# Continue building on the analysis
Use codex with sessionId "refactor-auth" to implement the security improvements you suggested

# Check session history
Use listSessions to see all active development sessions

Bug Fixing:

Use codex to help debug this error: [error message]

Code Generation:

Ask codex to create a React component that handles file uploads

Advanced Features (Codex CLI v0.50.0+)

Session Management

Key Features:

Native Resume: Leverages codex resume for optimal conversation continuity
Intelligent Defaults: GPT-5-Codex model for superior coding assistance
Fallback Context: Manual context building when resume unavailable
Session Persistence: Context maintained across interactions (24hr TTL)
Production-Ready: Comprehensive error handling and graceful degradation
Enterprise-Scale: 54 tests covering all functionality and edge cases

Model Selection & Control

Key Features:

Default GPT-5 Codex: Automatically uses the latest gpt-5-codex model for optimal coding assistance
Dynamic Models: Choose between different models per request
Reasoning Effort: Control AI processing depth (low/medium/high)
Per-Model Optimization: Optimized prompts for different model families
Flexible Configuration: Mix and match model and session parameters

Enhanced Authentication

Requirements:

⚠️ Breaking Change: Environment variable OPENAI_API_KEY no longer supported
New Setup: Run codex login --api-key "your-key" for authentication
Credential Storage: Credentials stored securely in CODEX_HOME/auth.json

Best Practices:

Use sessions with native resume for complex, multi-step development tasks
Default Model: Uses gpt-5-codex by default for optimal coding assistance
Choose appropriate reasoning effort: low for quick answers, high for complex analysis
Select models based on task complexity: gpt-5-codex for coding (default), gpt-4 for advanced reasoning, gpt-3.5-turbo for speed
Reset sessions when switching to unrelated topics
Check listSessions to manage active conversations

Development

# Install dependencies
npm install

# Development mode
npm run dev

# Build
npm run build

# Start built server
npm start

Documentation

📚 Comprehensive Guides

Session Management - Advanced session features and implementation details
Codex CLI Integration - v0.50.0+ features, breaking changes, and migration guide
API Reference - Complete tool documentation and usage examples

🔧 Development Resources

Testing Suite: 54 comprehensive tests covering all functionality
TypeScript Support: Full type definitions and IntelliSense
Error Handling: Robust error recovery and graceful degradation
Performance: Optimized for enterprise-scale usage

License

ISC