Course contents

Walkthrough

Install and Authenticate

Codex CLI on macOS / Linux, signing in, picking a model.

Watch · Riley Brown

A fast orientation of the Codex surface you just installed — panels, projects, preview, and the loop.

Steps · 0 / 4 done

Install via npm
Install the Codex CLI globally.
bash
```
npm install -g @openai/codex
```
Verifycodex --version prints a version.
Authenticate
Run codex once and pick "Sign in with ChatGPT" — usage is included with Plus/Pro/Team plans. Prefer pay-per-token? Set OPENAI_API_KEY in your shell instead.
bash
```
codex
```
VerifyAfter auth, the status line shows your account, model, and approval mode.
Pick a model for mobile work
gpt-5.1-codex-max is the agentic default and the right call for scaffolding. /model also sets reasoning effort — medium for iteration speed, high or xhigh when it must not miss.
prompt
```
/model gpt-5.1-codex-max
```
VerifyThe status line confirms the model and reasoning effort. You can switch mid-session at any time.
Give it project memory
Codex reads AGENTS.md — at repo root, in subfolders, and globally in ~/.codex — the same idea as CLAUDE.md from Course 1. Keep build commands and house rules there.
markdown
```
# AGENTS.md

- Expo app, TypeScript strict. Dev: `npx expo start`.
- Tests: `npm test`. Run them before declaring anything done.
- Never hand-edit ios/ or android/ — they're generated by prebuild.
```
VerifyA fresh session mentions your conventions without being told.

Check your understanding

Q1. Two valid ways to authenticate with Codex are…

· Tick off the 4 step(s) above.

· Score 100% on the quiz.

Vocabulary in this lesson

AGENTS.mdThe instructions file at the repo root that every session reads first: commands, conventions, gotchas. CLAUDE.md in Claude Code.

Plain-English definitions from the AI Coding Dictionary.