Codex · Concept

What Codex is and where things live

Codex is OpenAI's coding agent. An agent is an AI that can read files, edit code and run commands for you.
It runs in several places: the Codex CLI in your terminal, an extension in your code editor, the ChatGPT desktop app, and Codex Cloud. These lessons start with the CLI.
Codex comes with ChatGPT plans. Personal plans run from Free (limited) to Pro. Companies use Business or Enterprise, which don't train on business data by default. At work, use the workspace your company approved.
Open a terminal in your project folder and type codex. The first time, choose Sign in with ChatGPT and finish in your browser.
A chat is one conversation with Codex. /new starts a fresh one, /resume reopens a saved one and /exit leaves. AGENTS.md is a notes file Codex reads before it starts work. You'll write one in the next milestone.

Codex · ~/northwind-billing

>_ OpenAI Codex · model: gpt-6.1-sol medium · directory: ~/northwind-billing

Tell me about this project

This is Northwind's billing service. Invoices are built in src/invoice.ts, fees in src/fees.ts, and tests run with npm test. I didn't change anything.

Ask Codex to do anything

? for shortcuts

The banner shows the model and the folder Codex is working in. You type in the box at the bottom.