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Codex from Zero

OpenAI's terminal agent, Codex CLI: install and sign in, a first session you can undo, AGENTS.md, and the approvals and sandbox that decide what it may do. Free: 4 lessons in 1 level, about 29 minutes.

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Lesson 1 — Installing Codex CLI and signing in

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About 29 min left

⌘K — search the whole course: commands and glossary terms too.

Level 0. Install and first run

Sign in, a first session, AGENTS.md, approvals and the sandbox

0/4

We recommend taking these first: Terminal Basics.

What's nextWhich AI Coding Tool?Claude Code, Codex, Gemini CLI, Cursor, Grok, Kimi — what each is actually good at, and how to choose without burning a month.

More in this track: The tools

Claude Code from ZeroAnthropic's coding agent, end to end: install it, point it at a project, and get real work done.Claude Code: Pro LevelControl the session, permission modes and the sandbox, hooks and plugins, and Claude Code in scripts and CI — with safe limits.Which AI Coding Tool?Claude Code, Codex, Gemini CLI, Cursor, Grok, Kimi — what each is actually good at, and how to choose without burning a month.Gemini CLI from ZeroGoogle's open-source terminal agent: who should use it and who Antigravity CLI replaced it for, install and sign-in, a first session, GEMINI.md, and approval modes.

Frequently asked questions

Is "Codex from Zero" free?

Yes, the whole course is free — no ads, no paywall, no hidden charges. You can support the project if you want to, but it changes nothing about your access to the lessons.

Do I need to install anything or sign up?

Not for the course: every lesson runs in a terminal simulator in your browser, and your progress is saved in this browser. Using the real Codex CLI on your own projects is a separate step — you install it on your computer and sign in with a ChatGPT plan that includes Codex or with an OpenAI API key, which is billed at API rates. The first lesson of Level 0 walks through it.

Who is this course for?

After Terminal Basics. It picks up where Terminal Basics leaves off, so start there if you are new to it.

How many lessons is it, and how long will it take?

4 lessons. Go at your own pace — one short lesson a day, or several in a sitting.

Is there a certificate?

Yes. Finish every lesson and you unlock a personalized certificate you can share.