How to Use OpenAI Codex: Complete Terminal Guide for GPT-5-Codex Commands

OpenAI has just released GPT-5-Codex, a groundbreaking version of GPT-5 specifically optimized for agentic software engineering. This isn't just another code completion tool - it's a full-fledged AI coding partner that can work independently for hours, refactor entire codebases, and catch critical bugs before they ship.

Most importantly for developers, GPT-5-Codex brings unprecedented power directly to your terminal through a simple yet powerful command interface. This practical guide will show you exactly how to use Codex in your terminal, how to install OpenAI Codex CLI, and how to master the revolutionary cdx command.

The game-changer for developers is the new cdx command - a terminal interface that brings GPT-5-Codex's capabilities directly to your command line. Here's the essential function that powers it all:

Bash Code Example(9 lines)
CopyExpand
1cdx() {
2  if [[ "$1" == "update" ]]; then
3    npm install -g @openai/codex@latest
... 6 more lines
Click "Expand" to view the complete bash code

This simple function unlocks extraordinary capabilities:

• cdx update: Keeps your Codex CLI updated with the latest features and model improvements
• cdx [task]: Executes any coding task with GPT-5-Codex in full autonomous mode
• --full-auto: Enables complete autonomous operation - the model will handle complex tasks independently
• --model gpt-5-codex: Uses the new GPT-5-Codex model optimized for coding
• model_reasoning_summary_format=experimental: Activates enhanced reasoning display for better transparency

Step 1: Install Codex CLI Using npm

First, install the OpenAI Codex CLI globally using npm:

npm install -g @openai/codex@latest

Step 2: Add the cdx Function to Your Shell

Add the cdx function to your shell configuration file. For bash users, add to ~/.bashrc:

Bash Code Example(12 lines)
CopyExpand
1echo '
2cdx() {
3  if [[ "$1" == "update" ]]; then
... 9 more lines
Click "Expand" to view the complete bash code

For zsh users (macOS default), add to ~/.zshrc:

Bash Code Example(12 lines)
CopyExpand
1echo '
2cdx() {
3  if [[ "$1" == "update" ]]; then
... 9 more lines
Click "Expand" to view the complete bash code

Step 3: Authenticate with Your ChatGPT Account

Connect your ChatGPT account (Plus, Pro, Business, Edu, or Enterprise required):

codex auth

Example 1: Building a Complete Feature with Codex

cdx "Add a user authentication system with JWT tokens, password hashing, and email verification to my Express app"

GPT-5-Codex will:

• Analyze your existing codebase structure
• Install necessary dependencies (bcrypt, jsonwebtoken, nodemailer)
• Create authentication middleware
• Implement user models with proper schemas
• Set up email verification endpoints
• Add comprehensive error handling
• Write tests for all new functionality

Example 2: Massive Refactoring with OpenAI Codex

cdx "Refactor all database queries from callbacks to async/await pattern and add proper error handling"

Watch as GPT-5-Codex:

• Scans your entire codebase for database operations
• Converts callback patterns to modern async/await
• Adds try-catch blocks with contextual error messages
• Updates related tests to handle the new patterns
• Ensures backward compatibility

Example 3: Bug Detection and Security Fixes

cdx "Review my codebase for security vulnerabilities and fix any SQL injection risks"

GPT-5-Codex will:

• Perform comprehensive security analysis
• Identify potential SQL injection points
• Implement parameterized queries
• Add input validation and sanitization
• Generate a security report with explanations

Example 4: Automated Test Generation

cdx "Write comprehensive unit and integration tests for the payment processing module"

The model will:

• Analyze your payment module's API surface
• Create test fixtures and mocks
• Write unit tests for individual functions
• Add integration tests for payment flows
• Include edge cases and error scenarios

Working with Specific Files in Codex Terminal

cdx "Optimize the performance of src/api/handlers.js and add caching where appropriate"

Interactive Mode for Complex Tasks

Remove --full-auto for step-by-step approval:

codex --model gpt-5-codex -c model_reasoning_summary_format=experimental "Migrate database from MongoDB to PostgreSQL"

Custom Codex Configuration

Create a .codexrc file in your project root for project-specific settings:

Json Code Example(7 lines)
CopyExpand
1{
2  "model": "gpt-5-codex",
3  "autoApprove": ["read", "write"],
... 4 more lines
Click "Expand" to view the complete json code

Combining Codex with Git Workflows

Bash Code Example(5 lines)
CopyExpand
1# Create a feature branch and implement
2git checkout -b feature/user-dashboard
3cdx "Create a React dashboard component with user statistics, charts using D3.js, and real-time updates via WebSocket"
... 2 more lines
Click "Expand" to view the complete bash code

The performance improvements of GPT-5-Codex over standard GPT-5 are remarkable:

Accuracy Improvements:

• 74.5% accuracy on SWE-bench Verified (vs 51.3% for GPT-5)
• 51.3% success rate on complex refactoring tasks (vs 33.9%)
• 93.7% fewer tokens used for simple tasks (faster responses)
• 102.2% more reasoning on complex problems (better solutions)

Real-World Impact:

• Can work independently for 7+ hours on complex tasks
• Catches 3x fewer incorrect code review comments
• Generates 52.4% high-impact code review suggestions

Speed Optimizations:

• For simple tasks: GPT-5-Codex uses 93.7% fewer tokens
• For complex tasks: Spends 2x more time reasoning for better results
• Dynamically adjusts thinking time based on task complexity

GitHub Actions Integration with OpenAI Codex

Add GPT-5-Codex to your GitHub Actions workflow:

Yaml Code Example(17 lines)
CopyExpand
1name: AI Code Review
2on:
3  pull_request:
... 14 more lines
Click "Expand" to view the complete yaml code

Pre-commit Hooks for Automatic Code Improvement

Add automatic code improvement before commits:

Bash Code Example(3 lines)
CopyExpand
1#!/bin/sh
2# .git/hooks/pre-commit
3cdx "Review staged changes for common issues and fix any linting problems"
Click "Expand" to view the complete bash code

IDE Integration with Codex

GPT-5-Codex works seamlessly with VS Code, Cursor, and other IDEs through the Codex extension, maintaining context between terminal and editor sessions.

1. Security Configuration for OpenAI Codex

Always run Codex in sandboxed mode for untrusted code:

codex --sandbox --no-network "Analyze this third-party library for vulnerabilities"

2. Approval Workflows for Production Changes

For production changes, use explicit approval mode:

codex --model gpt-5-codex --require-approval "Deploy database migration to production"

3. Context Management for Better Results

Provide clear context files for better results:

Bash Code Example(5 lines)
CopyExpand
1echo "PROJECT_CONTEXT: E-commerce platform using Node.js, PostgreSQL, React
2CODING_STANDARDS: ESLint config, TypeScript strict mode
3DEPLOYMENT: AWS ECS with GitHub Actions" > .codex-context
... 2 more lines
Click "Expand" to view the complete bash code

4. Incremental Adoption Strategy

Start with low-risk tasks and gradually increase complexity:

1. Begin with code reviews and test generation
2. Move to bug fixes and small features
3. Progress to refactoring and architectural changes
4. Finally, enable autonomous operation for routine tasks

Daily Development Tasks with Codex CLI

Bash Code Example(15 lines)
CopyExpand
1# Morning setup
2cdx update
3cdx "Review yesterday's commits and suggest improvements"
... 12 more lines
Click "Expand" to view the complete bash code

Team Collaboration Using OpenAI Codex

Bash Code Example(8 lines)
CopyExpand
1# Code review assistance
2cdx "Review PR #234 focusing on security and performance"
3 
... 5 more lines
Click "Expand" to view the complete bash code

Issue: cdx Command Not Found

If cdx command is not recognized:

Bash Code Example(5 lines)
CopyExpand
1# Verify installation
2npm list -g @openai/codex
3 
... 2 more lines
Click "Expand" to view the complete bash code

Issue: Codex Authentication Failed

Bash Code Example(3 lines)
CopyExpand
1# Re-authenticate
2codex auth --reset
3codex auth
Click "Expand" to view the complete bash code

Issue: Model Timeout on Large Tasks

For complex operations, increase timeout:

codex --model gpt-5-codex --timeout 3600 "Refactor entire authentication system"

Issue: Permission Errors

Ensure proper npm permissions:

Bash Code Example(5 lines)
CopyExpand
1# Fix npm permissions
2sudo chown -R $(whoami) $(npm config get prefix)/{lib/node_modules,bin,share}
3 
... 2 more lines
Click "Expand" to view the complete bash code

GPT-5-Codex represents a paradigm shift in how we interact with AI for coding. The cdx command brings enterprise-grade AI capabilities directly to your terminal, where real development happens. This isn't about replacing developers - it's about amplifying their capabilities.

With GPT-5-Codex, a single developer can now:

• Maintain code quality across massive codebases
• Implement complex features in minutes instead of hours
• Catch bugs before they reach production
• Refactor legacy code with confidence
• Generate comprehensive tests automatically

The terminal interface ensures you maintain full control while leveraging AI that can work autonomously for hours when needed. It's the perfect balance of power and practicality.

Ready to revolutionize your development workflow? Here's your quick start guide:

1. Install Codex CLI: npm install -g @openai/codex@latest
2. Add the cdx function to your shell configuration
3. Authenticate: codex auth
4. Try your first command: cdx "Help me understand this codebase"

GPT-5-Codex is included with ChatGPT Plus, Pro, Business, Edu, and Enterprise plans. Pro users can support a full workweek of intensive coding, while Business and Enterprise plans can purchase additional credits for team-wide adoption.

Pricing and Availability

• ChatGPT Plus: Includes basic Codex access for individual developers
• ChatGPT Pro: Full workweek of intensive coding support
• ChatGPT Business: Team licenses with credit pools
• ChatGPT Enterprise: Unlimited usage with dedicated support

The age of AI-powered terminal coding has arrived. With the simple cdx command, you're not just writing code - you're orchestrating an AI partner that understands your intent, maintains your standards, and delivers production-ready solutions. Welcome to the future of software development with OpenAI Codex.