Confirm it's really there

Same move you used for the Claude CLI. Don't trust "no error message." Check directly. In your terminal, type:

codex --version

If the install worked, this prints a version number and quits. A version number is the whole confirmation: Codex is installed and your terminal can find it.

If it says command not found

If codex --version prints command not found: codex, run the same playbook you learned for the Claude CLI:

1. Close the terminal window completely and open a fresh one. A terminal only learns about new commands when it starts. A window that was open during the install hasn't noticed codex yet. This fixes it most of the time. Run codex --version again in the new window.
2. If a fresh window still fails, the install didn't fully land. Re-run the install command for your path (the brew line or the npm i -g @openai/codex line). Watch its output this time for any line that actually says "error."
3. If you took the npm path and it still fails, double-check Node: run node --version. If that's missing too, Node didn't install, and that's the thing to fix first.

Notice the pattern: the troubleshooting is the same as the Claude CLI's, because the underlying issue is the same one (a terminal not yet aware of a new command). Skills you build in one tool keep paying off in the next. That's the whole reason the second tool is cheap to learn.

Once codex --version prints a number, you're installed. Next: signing in.