Codex MCP Server

Advanced MCP server wrapper for OpenAI Codex CLI v0.36.0+ that provides enterprise-grade conversational AI coding assistance with session management, intelligent model selection, and native resume functionality.

Prerequisites

  • OpenAI Codex CLI v0.36.0+ 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

  • Claude Code installed

Installation

One-Click Installation

VS Code

Install in VS Code

VS Code Insiders

Install in VS Code Insiders

Cursor

Install in 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 v0.36.0+)

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

🔧 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

Nextdocs

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