Codex

OpenAI’s agent. Mac app, terminal, and a cloud that works while you sleep.

Codex is OpenAI's coding agent, and it comes with the subscription a lot of people already have: ChatGPT Plus. If that's you, you own a coding agent right now and maybe didn't know it. Under the hood it runs a coding-tuned GPT-5-Codex model, so you rarely have to think about model choice at all.

Two ways to run it

The app: download the Codex desktop app from developers.openai.com/codex, sign in with your ChatGPT account, and point it at a project folder. No terminal involved. It's a regular Mac app with an agent inside.

The terminal: one paste, using the Node you installed in Setup:

npm install -g @openai/codex

Then start it inside any project folder:

cd my-project
codex

What makes it distinctive

• –The cloud. Hand a task (or several, in parallel) to Codex's cloud environment, close your laptop, and review finished work later. No other mainstream tool makes delegation feel this literal.
• –Subagents. For big jobs Codex can spawn specialist helpers that work in parallel and report their results back in one response, which is ideal for exploring a codebase or building out a multi-step plan.
• –Project memory. Codex reads a file called AGENTS.md at your project root: its standing notes about your project. It'll build one as you work.

A first prompt that shows off the species:

Tell me about this project. Then find the three most obvious problems and fix them one at a time, explaining each fix in plain English.

And take the advice OpenAI's own docs give: have the agent save a checkpoint before and after big tasks. That habit gets a whole section later (Safety nets), so start building it now.

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