THE SHORT ANSWER
How to use Codex without losing control of your code
Treat Codex like a capable junior engineer with excellent speed and imperfect judgment. Give it a bounded task, provide acceptance criteria, and review the diff before merging.
- Describe the outcome and acceptance criteria, not just the file you want changed.
- Ask Codex to inspect first and explain its plan.
- Use tests, linting, and a pull request review before deployment.
What Codex is for
OpenAI describes Codex as an AI agent that helps write, review, and ship code. It is most useful when the work spans several files and the result can be checked with tests or a clear visual result. Sources: Codex overview, Using Codex with ChatGPT
A good prompt
State the current behaviour, desired behaviour, constraints, files that may be relevant, and the command that proves the change works. Ask it to avoid unrelated refactors.
The review step
Read the diff as if someone else submitted it. Check permissions, data handling, error states, and whether tests cover the actual bug. Speed only matters when the result is safe to use.