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.
Latest Release (v1.2.4): Enhanced Windows compatibility - Now using cross-spawn for reliable npm global command execution across all platforms (Windows, macOS, Linux). See changelog
- 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:
✅ Cross-Platform Support: Fully tested and working on Windows, macOS, and Linux (v1.2.4+)
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:
- Add to your Claude Desktop config:
"codex-cli": {
"command": "npx",
"args": ["-y", "@cexll/codex-mcp-server"]
}
- 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
- macOS:
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-clito 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 doesuse codex to summarize @. the current directoryanalyze @package.json and list dependencies
General Questions (without files)
ask codex to explain div centeringask 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 methoduse codex to brainstorm 10 innovative features for our app with feasibility analysisask 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 tofullAuto: true)sandbox: false(default) → Does NOT disable sandboxing, just doesn't enable auto mode- Important: The
sandboxparameter is a convenience flag, not a security control
Granular Control Parameters:
sandboxMode: Controls file system access levelapprovalPolicy: Controls when user approval is requiredfullAuto: Shorthand forsandboxMode: "workspace-write"+approvalPolicy: "on-failure"yolo: ⚠️ Bypasses all safety checks (dangerous, not recommended)
Sandbox Modes
| Mode | Description | Use Case |
|---|---|---|
read-only | Analysis only, no file modifications | Code review, exploration, documentation reading |
workspace-write | Can modify files in workspace | Most development tasks, refactoring, bug fixes |
danger-full-access | Full system access including network | Advanced automation, CI/CD pipelines |
Approval Policies
| Policy | Description | When to Use |
|---|---|---|
never | No approvals required | Fully trusted automation |
on-request | Ask before every action | Maximum control, manual review |
on-failure | Only ask when operations fail | Balanced automation (recommended) |
untrusted | Maximum paranoia mode | Untrusted code or high-risk changes |
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
approvalPolicyis set butsandboxModeis not → auto-setssandboxMode: "workspace-write" - ✅ If
search: trueoross: true→ auto-setssandboxMode: "workspace-write"(for network access) - ✅ All commands include
--skip-git-repo-checkto 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
Common Issues
Issue 1: MCP Tool Timeout Error
If you encounter timeout errors when using Codex MCP tools:
# Set the MCP tool timeout environment variable (in milliseconds)
export MCP_TOOL_TIMEOUT=36000000 # 10 hours
# For Windows (PowerShell):
$env:MCP_TOOL_TIMEOUT=36000000
# For Windows (CMD):
set MCP_TOOL_TIMEOUT=36000000
Add this to your shell profile (~/.bashrc, ~/.zshrc, or PowerShell profile) to make it permanent.
Issue 2: Codex Cannot Write Files
If Codex responds with permission errors like "Operation blocked by sandbox policy" or "rejected by user approval settings", configure your Codex CLI settings:
Create or edit ~/.codex/config.toml:
# Dynamically generated Codex configuration
model = "gpt-5-codex"
model_reasoning_effort = "high"
model_reasoning_summary = "detailed"
approval_policy = "never"
sandbox_mode = "danger-full-access"
disable_response_storage = true
network_access = true
⚠️ Security Warning: The danger-full-access mode grants Codex full file system access. Only use this configuration in trusted environments and for tasks you fully understand.
Configuration File Locations:
- macOS/Linux:
~/.codex/config.toml - Windows:
%USERPROFILE%\.codex\config.toml
After updating the configuration, restart your MCP client (Claude Desktop, Claude Code, etc.).
Basic Examples
use codex to create and run a Python script that processes dataask codex to safely test @script.py and explain what it does
Default Behavior:
- All
codex execcommands automatically include--skip-git-repo-checkto 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 viacodex exec.- Supports
@file references for including file content - Optional
modelparameter - 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=trueenables--full-automodechangeMode=truereturns structured OLD/NEW edits- Supports approval policies and sandbox modes
- Automatically includes
--skip-git-repo-checkto prevent permission errors in non-git environments
- Supports
-
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
cacheKeyandchunkIndexparameters
-
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 dataor/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.
Recent Updates
v1.2.4 (2025-10-27)
🔧 Major Improvement:
- Windows Compatibility Enhancement: Replaced Node.js native
spawn()with industry-standardcross-spawnpackage- Root cause: Previous
shell: truefix still failed on some Windows configurations - Solution: Use
cross-spawn(50M+ weekly downloads, used by Webpack/Jest) for automatic Windows.cmdhandling - Benefits:
- Zero configuration required for Windows users
- Automatic handling of
.cmd,.ps1, and.exeextensions - Compatible with both CMD and PowerShell environments
- <5ms performance overhead
- Dependencies: Added
cross-spawn@^7.0.6and@types/cross-spawn
- Root cause: Previous
🐛 Bug Fixes:
- Enhanced ENOENT error diagnostics with Windows-specific 4-step troubleshooting guide
- Added optional chaining for
stdout/stderrto handle null values in TypeScript strict mode
📝 Documentation:
- Added comprehensive Windows troubleshooting section in docs
- Documented
spawn codex ENOENTerror resolution steps
v1.2.3 (2025-10-27)
🐛 Bug Fixes:
- Windows Compatibility: Fixed Codex CLI detection failing on Windows despite proper installation
- Root cause:
spawn()withshell: falsecouldn't resolve.cmdextensions on Windows - Solution: Enabled shell mode for cross-platform command execution
- Impact: Zero performance impact (~10ms overhead), maintains security with array-form arguments
- Platforms verified: Windows, macOS, Linux via GitHub Actions CI
- Root cause:
📝 Documentation:
- Updated all package references from
@trishchuk/codex-mcp-toolto@cexll/codex-mcp-server - Enhanced cross-platform setup instructions
🔍 Testing:
- CI/CD now validates on Ubuntu, macOS, and Windows across Node.js 18.x, 20.x, and 22.x
v1.2.2 & Earlier
- Smart sandbox mode defaults to prevent permission errors
- Enhanced debug information for troubleshooting
- Automatic
--skip-git-repo-checkflag for non-git environments - Web search integration with feature flags
- Structured change mode with pagination support
Platform Support
| Platform | Status | Notes |
|---|---|---|
| Windows | ✅ Fully Supported | Enhanced in v1.2.4 with cross-spawn |
| macOS | ✅ Fully Supported | Tested on Darwin 23.5.0+ |
| Linux | ✅ Fully Supported | Tested on Ubuntu Latest |
Minimum Requirements:
- Node.js v18.0.0 or higher
- Codex CLI installed and authenticated (
npm install -g @openai/codex)
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.