Codex MCP Tool

Codex MCP Tool

Codex MCP Tool is an open‑source Model Context Protocol (MCP) server that connects your IDE or AI assistant (Claude, Cursor, etc.) to the Codex CLI. It enables non‑interactive automation with codex exec, safe sandboxed edits with approvals, and large‑scale code analysis via @ file references. Built for reliability and speed, it streams progress updates, supports structured change mode (OLD/NEW patch output), and integrates cleanly with standard MCP clients for code review, refactoring, documentation, and CI automation.

• Ask Codex questions from your MCP client, or brainstorm ideas programmatically.

TLDR: + Codex CLI

Goal: Use Codex directly from your MCP-enabled editor to analyze and edit code efficiently.

Prerequisites

Before using this tool, ensure you have:

1. Node.js (v18.0.0 or higher)
2. Codex CLI installed and authenticated

One-Line Setup

claude mcp add codex-cli -- npx -y @cexll/codex-mcp-server

Verify Installation

Type /mcp inside Claude Code to verify the Codex MCP is active.

Alternative: Import from Claude Desktop

If you already have it configured in Claude Desktop:

1. Add to your Claude Desktop config:

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

2. Import to Claude Code:

claude mcp add-from-claude-desktop

Configuration

Register the MCP server with your MCP client:

For NPX Usage (Recommended)

Add this configuration to your Claude Desktop config file:

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

For Global Installation

If you installed globally, use this configuration instead:

{
  "mcpServers": {
    "codex-cli": {
      "command": "codex-mcp"
    }
  }
}

Configuration File Locations:

• Claude Desktop:
  • macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
  • Windows: %APPDATA%\Claude\claude_desktop_config.json
  • Linux: ~/.config/claude/claude_desktop_config.json

After updating the configuration, restart your terminal session.

Example Workflow

• Natural language: "use codex to explain index.html", "understand this repo with @src", "look for vulnerabilities and suggest fixes"
• Claude Code: Type /codex-cli to access the MCP server tools.

Usage Examples

Model Selection

// Use the default gpt-5-codex model
'explain the architecture of @src/';

// Use gpt-5 for fast general purpose reasoning
'use codex with model gpt-5 to analyze @config.json';

// Use o3 for deep reasoning tasks
'use codex with model o3 to analyze complex algorithm in @algorithm.py';

// Use o4-mini for quick tasks
'use codex with model o4-mini to add comments to @utils.js';

// Use codex-1 for software engineering
'use codex with model codex-1 to refactor @legacy-code.js';

With File References (using @ syntax)

• ask codex to analyze @src/main.ts and explain what it does
• use codex to summarize @. the current directory
• analyze @package.json and list dependencies

General Questions (without files)

• ask codex to explain div centering
• ask codex about best practices for React development related to @src/components/Button.tsx

Brainstorming & Ideation

• brainstorm ways to optimize our CI/CD pipeline using SCAMPER method
• use codex to brainstorm 10 innovative features for our app with feasibility analysis
• ask codex to generate product ideas for the healthcare domain with design-thinking approach

Codex Approvals & Sandbox

Codex CLI supports fine-grained control over permissions and approvals through sandbox modes and approval policies.

Understanding Parameters

The sandbox Parameter (Convenience Flag):

• sandbox: true → Enables fullAuto mode (equivalent to fullAuto: true)
• sandbox: false (default) → Does NOT disable sandboxing, just doesn't enable auto mode
• Important: The sandbox parameter is a convenience flag, not a security control

Granular Control Parameters:

• sandboxMode: Controls file system access level
• approvalPolicy: Controls when user approval is required
• fullAuto: Shorthand for sandboxMode: "workspace-write" + approvalPolicy: "on-failure"
• yolo: ⚠️ Bypasses all safety checks (dangerous, not recommended)

Sandbox Modes

Approval Policies

Configuration Examples

Example 1: Balanced Automation (Recommended)

{
  "approvalPolicy": "on-failure",
  "sandboxMode": "workspace-write",  // Auto-set if omitted in v1.2+
  "model": "gpt-5-codex",
  "prompt": "refactor @src/utils for better performance"
}

Example 2: Quick Automation (Convenience Mode)

{
  "sandbox": true,  // Equivalent to fullAuto: true
  "model": "gpt-5-codex",
  "prompt": "fix type errors in @src/"
}

Example 3: Read-Only Analysis

{
  "sandboxMode": "read-only",
  "model": "gpt-5-codex",
  "prompt": "analyze @src/ and explain the architecture"
}

Smart Defaults (v1.2+)

Starting from version 1.2.0, the server automatically applies intelligent defaults to prevent permission errors:

• ✅ If approvalPolicy is set but sandboxMode is not → auto-sets sandboxMode: "workspace-write"
• ✅ If search: true or oss: true → auto-sets sandboxMode: "workspace-write" (for network access)
• ✅ All commands include --skip-git-repo-check to prevent errors in non-git environments

Troubleshooting Permission Errors

If you encounter ❌ Permission Error: Operation blocked by sandbox policy:

Check 1: Verify sandboxMode

# Ensure you're not using read-only mode for write operations
{
  "sandboxMode": "workspace-write",  // Not "read-only"
  "approvalPolicy": "on-failure"
}

Check 2: Use convenience flags

# Let the server handle defaults
{
  "sandbox": true,  // Simple automation
  "prompt": "your task"
}

Check 3: Update to latest version

# v1.2+ includes smart defaults to prevent permission errors
npm install -g @cexll/codex-mcp-server@latest

Basic Examples

• use codex to create and run a Python script that processes data
• ask codex to safely test @script.py and explain what it does

Default Behavior:

• All codex exec commands automatically include --skip-git-repo-check to avoid unnecessary git repository checks, as not all execution environments are git repositories.
• This prevents permission errors when running Codex in non-git directories or when git checks would interfere with automation.

Advanced Examples

// Using ask-codex with specific model
'ask codex using gpt-5 to refactor @utils/database.js for better performance';

// Brainstorming with constraints
"brainstorm solutions for reducing API latency with constraints: 'must use existing infrastructure, budget under $5k'";

// Change mode for structured edits
'use codex in change mode to update all console.log to use winston logger in @src/';

Tools (for the AI)

These tools are designed to be used by the AI assistant.

Core Tools

• ask-codex: Sends a prompt to Codex via codex exec.

  • Supports @ file references for including file content
  • Optional model parameter - available models:
    • gpt-5-codex (default, optimized for coding)
    • gpt-5 (general purpose, fast reasoning)
    • o3 (smartest, deep reasoning)
    • o4-mini (fast & efficient)
    • codex-1 (o3-based for software engineering)
    • codex-mini-latest (low-latency code Q&A)
    • gpt-4.1 (also available)
  • sandbox=true enables --full-auto mode
  • changeMode=true returns structured OLD/NEW edits
  • Supports approval policies and sandbox modes
  • Automatically includes --skip-git-repo-check to prevent permission errors in non-git environments

• brainstorm: Generate novel ideas with structured methodologies.

  • Multiple frameworks: divergent, convergent, SCAMPER, design-thinking, lateral
  • Domain-specific context (software, business, creative, research, product, marketing)
  • Supports same models as ask-codex (default: gpt-5-codex)
  • Configurable idea count and analysis depth
  • Includes feasibility, impact, and innovation scoring
  • Example: brainstorm prompt:"ways to improve code review process" domain:"software" methodology:"scamper"

• ping: A simple test tool that echoes back a message.

  • Use to verify MCP connection is working
  • Example: /codex-cli:ping (MCP) "Hello from Codex MCP!"

• help: Shows the Codex CLI help text and available commands.

Advanced Tools

• fetch-chunk: Retrieves cached chunks from changeMode responses.

  • Used for paginating large structured edit responses
  • Requires cacheKey and chunkIndex parameters

• timeout-test: Test tool for timeout prevention.

  • Runs for a specified duration in milliseconds
  • Useful for testing long-running operations

Slash Commands (for the User)

You can use these commands directly in Claude Code's interface (compatibility with other clients has not been tested).

• /analyze: Analyzes files or directories using Codex, or asks general questions.
  • prompt (required): The analysis prompt. Use @ syntax to include files (e.g., /analyze prompt:@src/ summarize this directory) or ask general questions (e.g., /analyze prompt:Please use a web search to find the latest news stories).
• /sandbox: Safely tests code or scripts with Codex approval modes.
  • prompt (required): Code testing request (e.g., /sandbox prompt:Create and run a Python script that processes CSV data or /sandbox prompt:@script.py Test this script safely).
• /help: Displays the Codex CLI help information.
• /ping: Tests the connection to the server.
  • message (optional): A message to echo back.

Acknowledgments

This project was inspired by the excellent work from jamubc/gemini-mcp-tool. Special thanks to @jamubc for the original MCP server architecture and implementation patterns.

Contributing

Contributions are welcome! Please submit pull requests or report issues through GitHub.

License

This project is licensed under the MIT License. See the LICENSE file for details.

Disclaimer: This is an unofficial, third-party tool and is not affiliated with, endorsed, or sponsored by OpenAI.