Instrument: Codex

Codex is ChatGPT’s hands in your folder

Grok Build is a parallel door, not a rival church. Same PROJECT.md. Different nameplate. Grok tutorial.

Do not drown

Five surfaces, one family

OpenAI ships several doors. You only need one to start.

ChatGPT

The chat site and apps. Good for planning and talking. Limited Codex on free; more on Plus/Pro.

Codex CLI

You type codex in a terminal inside your project folder. This tutorial is that door.

IDE extension

Codex as a panel inside VS Code or similar. Same agent, different skin.

Desktop app

ChatGPT’s desktop app can host Chat, Codex, and Work as modes. Same account. Different tab.

Work

Agent-style tasks in the ChatGPT product. Useful later. Not required to type codex today.

Official map: Codex CLI docs. Pricing for the family: official Codex docs list Free $0, Go $8, Plus $20, Pro from $100.

Install

Official installer (macOS / Linux)

This line is from OpenAI’s Codex CLI docs. Windows: use the Windows tab on that same page rather than a guessed one-liner — packaging moves.

macOS / Linux 
$ curl -fsSL https://chatgpt.com/codex/install.sh | sh
Expected

Installer finishes. Then codex is a real command.

What did I just do?

You installed OpenAI’s coding agent onto this computer. You have not touched your project files yet.

If it fails

Need a ChatGPT sign-in the first time you run codex. Free/Go have limited Codex; Plus and Pro have more. See Codex pricing. Windows users: follow the current Windows instructions on the CLI page (native PowerShell or WSL).

Launch

Open the folder, then type codex

Same VS Code move as Grok: Terminal → New Terminal. If Copilot CLI waves at you, that is still a different instrument.

inside the project folder 
PS C:\my-app> codex
Expected

A Codex session. Official docs show a TUI with a model line (for example gpt-5.6-sol) and a prompt. First run: sign in with ChatGPT.

What did I just do?

Codex is now attached to this working directory. It can inspect files, edit them, and run local tools. That is why PROJECT.md’s “never without approval” list exists.

AGENTS.md

Codex’s nameplate, not a second brain

Codex looks for AGENTS.md. Copy adapters/AGENTS.md from the kit to the project root. It says “read PROJECT.md.” Official CLI also has /init to create an AGENTS.md — if you use that, keep it thin. Do not let it become a fork of the spec.

inside Codex 
Read PROJECT.md. Do not write code yet.
Write a numbered Phase 1 plan.
After each step include: what will be built, how I will test it, and any command.
Wait for my approval.
Expected

A plan you can reject. If files start changing, interrupt and paste this again.

What did I just do?

Same first sentence as Grok. Instruments are interchangeable at this gate. You are not.