The OpenAI Codex is a specialized artificial intelligence system designed to translate natural language into code.
We have just published a course. freeCodeCamp.org YouTube channel that will teach you how to use Codex to accelerate real-world coding workflows and developer productivity. Andrew Brown from ExamPro developed this course.
Introduction
Codex Essentials
AI Certification Roadmap
Study recommendations and passing requirements
Validation and recertification
Access to Code Repository Codex Fundamentals
What is Codex? Agentive Coding vs Coding Harness
Common use cases and skills
Understanding the agency loop
Open AIGPT model families
Deep Dive: Model Intelligence vs. Contextual Windows
Installation Requirements (Node.js and WSL 2)
Authentication: Subscription vs. API Keys
Checking login status and account information.
Lab: Installing Codex and “Hello World”.
Using API keys for production and automation
Setting environment variables for keys
Subscriptions vs. API Token Billing
Managing context windows (400k token limits)
Problems with truncation and hallucinations
Commands: /clear and /compact
Lab: Managing Contextual History
Codex sessions, threads, and messages
Session commands: /new, /resume, /fork, and /rename.
Under the hood: SQLite and JSONL session storage
Usage tracking with custom scripts
Customizing the status line
Project guidance by agents.md
Deduction Limits and Tracing
Lab: Creating Project Guidelines
Deep Dive: Plan mode and clarifying questions
Project Lab: Creating a Wolfenstein 3D clone
Sandbox Security: Bubble wrap and seat belts
Approval policies (distrust, request, never)
OS-specific settings and network access
Permission Overrides: Auto Mode vs Full Access
Creating and troubleshooting rules
Global vs. project configuration (config.toml) API, SDKs, and extensions
Non-interactive (headless) mode for CI/CD
OpenAI Interaction Layers: REST API vs. SDKs
Implementing the OpenAI Agents SDK
Working with the Codex SDK
Using the Codex desktop application
Installing VS Code Extensions
Codex App Server Protocol
Automate workflows with GitHub Actions
The Anatomy of Agent Expertise.
Discovery, Activation, and Implementation
Areas of expertise and markets
Lab: Image Generation Skills
Project Lab: Building Task Manager Skills
Optimizing costs with model and effort selection
Fast mode for guessing
Integrating MCP Tools (Roblox Example)
Orchestrating sub-agents and worker teams.