OpenAI's Codex, a cloud-based programming intelligence designed for software engineers, is changing the daily workflow of developers. This tutorial goes straight into the practical aspects of setting up, using, and mastering Codex's features to make your development more efficient.

Quick Setup Guide

To start using Codex, you need to complete a series of account authorizations and environment configurations. Below is the detailed setup process:

Account Privileges and Pre-requisites

Currently (May 2025), Codex is only available to the following users:

• ChatGPT Pro users ($200 per month)
• ChatGPT Enterprise users
• ChatGPT Team users

Note: ChatGPT Plus and Edu users are expected to have access to this feature soon.

Setup Steps in Detail

• Accessing the Codex Entry
  • Log in to your ChatGPT account
  • Find the Codex option in the sidebar
  • Clicking on it will take you to the separate Codex application page

• Enabling Multi-Factor Authentication (MFA)
  • Codex requires your account to be MFA enabled.
  • Can use any authentication app like Google Authenticator, OnePass, etc.
  • This is a security measure because Codex will gain access to your GitHub repository!

• GitHub Account Association
  • Authorize Codex to access your GitHub account
  • Select organizational access rights (if applicable to your situation)
  • Setting the range of access rights (read-only or read-write access)
  • Note: Codex will be able to create PRs if you grant read and write permissions.

• Data usage settings
  • During the setup process, there will be a data authorization option
  • By default, Codex will use your code for training
  • If you don't want your code to be used for training, you need to uncheck it manually

Once you've completed the above steps, you're ready to start selecting code repositories and using Codex. The entire setup process is designed to be very intuitive and easy even for first-time developers.

Interface and Basic Operation

After successfully setting up the Codex, you will be presented with an intuitive user interface that allows us to understand how to perform basic operations.

Main interface overview

The main interface of Codex contains the following key elements:

• Repository selector: for switching between different GitHub repositories
• Task list: displays current and historical tasks
• Task type selector: for selecting Ask or Code mode
• Task input box: enter a description of the task you want to perform

Two core mission models

Codex offers two different modes of operation, each suitable for different scenarios:

1. Ask mode
   • For querying and understanding the code base
   • No code will be changed
   • Ideal for understanding the structure of a project, seeking explanations or exploring the code base
   • Example: Ask about the total lines of code of the project, code structure analysis, etc.
2. Code mode
   • For performing actual code modification tasks
   • Code will be modified and changes will be generated in a cloud environment
   • Good for fixing bugs, adding features, refactoring code, etc.
   • Allows creation of Pull Requests to commit changes

Create and manage tasks

To create a new task, the steps are as follows:

1. Select the type of task (Ask or Code)
2. Describe your mission in the input box
3. For first-time users, you can click directly on the preset sample tasks
4. Click the "Start Task" button to submit the task.

After submitting, Codex will start processing your task and display real-time progress. Each task is managed in a separate page and you can run multiple tasks in parallel.

View task results

After the task is completed, you will see the detailed results of the execution:

• For Ask mode: get detailed answers to questions
• For Code mode: view code changes, terminal output and test results

For Code tasks, you can still:

• Creating a GitHub PR: Committing changes to the repository as a PR
• Request for further modifications: give feedback to allow Codex to adapt its solution
• View detailed execution logs and chain of evidence

Full process of task submission and execution

Let's walk through a real-world example of how to use Codex to accomplish a simple code fixing task.

Choosing the right warehouse

First, choose a GitHub repository you're familiar with from the main Codex interface. Ideally, choose:

• Well-documented projects
• Items included for testing
• Simple dependency structure

This makes it easier for Codex to understand and perform tasks.

Submit a Code Task

1. Selecting "Code" Mode
2. Enter it in the task description: Explaining the codebase to newbies. What is the general structure, what are the important things to know, and what are some of the next key points to learn.
3. Click on the "Start Task" button.

Tracking the progress of tasks

After submitting a task, you can watch Codex work in real time:

• Codex will first analyze the code base structure
• Then search for files in the specified directory
• Checking for spelling and syntax problems in the code
• Apply fixes and run tests to verify

The whole process can take several minutes, depending on the size and complexity of the code base.

Review results and create PR

After the task is completed, you will see the results of Codex's work:

• What documents have been modified
• What exactly was fixed
• Test Passing Status

If you're happy with the results, you can click the "Create PR" button and Codex will automatically create a Pull Request with the changes, and then you can go back to GitHub and follow the usual process of reviewing and merging the PR.

With this simple example, you can see how Codex can be seamlessly integrated into your development workflow to help with everyday coding tasks.

Advanced Usage Tips

To realize the full potential of Codex, it's important to have some advanced tips and best practices.

Cue word engineering

Writing high-quality task descriptions (prompts) is the key to getting the most out of your Codex. Here are some practical tips:

Optimized configuration of projects

To make Codex work more efficiently, you can add auxiliary information to your project:

Add the AGENTS.md file

In the project root directory, create the AGENTS.md document that provides program guidance for AI intelligences, including:

• Description of the project structure
• Coding Norms and Style Guides
• Test Run Method
• PR Creation Rules
• Development Process Description

Example AGENTS.md contents:

## Project Structure
- src/api: API endpoint definition
- src/components: React components
- src/utils: Generic utility functions

## Testing Guide
- Run `npm test` to run all tests.
- Every feature must have unit tests

## PR Specification
- Title Format: [Module] Brief Description
- Must pass all lint checks and tests

Environmental constraints and precautions

The following restrictions apply when using Codex:

1. No Internet access
   • Codex Runtime Environment cannot access the external network
   • Unable to install new dependency packages (e.g. npm install (Invalid)
   • Only use code and pre-installed dependencies that are already in the project.
2. Environment Configuration
   • Environment scripts can be customized through advanced settings
   • Required dependencies and environments need to be configured in advance
3. task isolation
   • Each task runs in a separate environment and does not share state
   • No direct interaction between multiple tasks

Application Scenarios and Practical Case Studies

Based on actual development needs, Codex can provide effective help in a variety of scenarios. Below are some typical use cases and the corresponding task design methods.

Code Review and Optimization

Scene Description: Check code quality and suggest improvements

Mandate format::

Please review the src/components/UserProfile.tsx file to analyze possible performance issues and suggest improvements. Pay special attention to the risk of unnecessary rendering and memory leaks.

Elements of implementation::

• Requests for specific, actionable recommendations rather than generalizations
• Specify concerns (e.g., performance, security, maintainability)
• Requirements for evidence or explanations, not just conclusions

Complex Bug Diagnosis and Repair

Scene Description: Fixing hard-to-recover conditional errors

Mandate format::

Occasionally the following error occurs when a user modifies multiple fields at the same time and saves them quickly:
TypeError: Cannot read properties of undefined (reading 'email')
at validateUserInput (/app/src/utils/validation.ts:41)

Please analyze the possible causes and fix this issue to ensure that it works properly even in asynchronous operation competitive conditions.

Elements of implementation::

• Provide complete error stack information
• Describe the specific scenarios and conditions under which the error occurred
• Clarify acceptance criteria for the restoration (e.g. what tests should be passed)

Specialized field programming

Scene Description: Code generation for specific domains (e.g. hardware description languages)

Mandate format::

Design a Verilog module for an 8-bit RISC processor containing the following instruction sets: ADD, SUB, AND, OR, XOR, LOAD, STORE, JUMP. ensure that the timing is correct and synthesizable.

Elements of implementation::

• Provide clear technical specifications
• Specify the verification method (e.g., simulation testing)
• Requirements are in line with industry standard practices

Automated Test Generation

Scene Description: Create test suites for newly implemented features

Mandate format::

Generate unit tests for all public methods in the src/services/authentication.js file. Make sure the tests include normal paths, error handling and edge cases. Use the Jest test framework and test styles already in the project.

Elements of implementation::

• Clarify testing framework and style requirements
• Specify the method or function to be tested
• Requirements to cover different types of test scenarios

Practical Tips Summary

Based on feedback from developers who have actually used Codex, the following practices can significantly improve efficiency:

1. task batch processing
   • Submitting a small batch of tasks every morning for Codex to process in parallel
   • Come back and review the results directly rather than waiting for each task
2. Progressive tasks
   • Let Codex analyze the problem first.
   • Refinement of follow-up tasks based on analysis
   • Step-by-step solutions
3. Exploratory Development
   • Let Codex try multiple solutions at once
   • Comparing the advantages and disadvantages of different programs
   • Selection of the best program for implementation
4. Integration with team workflows
   • Have Codex perform code review before PR review
   • Use Codex to generate initial documentation, then refine it manually
   • Let Codex handle routine maintenance tasks such as dependency updates, style adjustments, etc.

With these practical examples and tips, you can effectively integrate Codex into your daily development process, making it your programming assistant, handling tedious tasks and improving overall development efficiency.