How to Use Codex for Code Review

Codex is useful as a reviewer because it can read the diff, inspect surrounding files, compare intent to implementation, and look for missing tests.

The mistake is asking for "thoughts." Ask for review findings. Make it lead with risks, not compliments.

Quick picks

Best review prompt: Find bugs first. A review that starts with praise usually misses the point.
Best scope: One PR or one focused diff. The review improves when Codex can reason about the whole change without boiling the ocean.
Best output: Findings, questions, summary. This mirrors useful human code review.
Best follow-up: Ask for tests. Many AI-written changes fail at the edge cases, not the happy path.

Use a review stance, not a helper stance

When you ask Codex to review, tell it to prioritize bugs, regressions, missing tests, security/privacy risk, accessibility, performance, and unclear behavior.

Do not ask it to "make this better" until it has identified what is actually wrong.

Make it inspect context

A diff alone can be misleading. Ask Codex to read the surrounding files, existing tests, and related patterns before deciding whether something is a bug.

The best finding has a reason. The best false positive gets discarded before it reaches you.

Ask for missing tests separately

Codex often finds different issues when you ask specifically for test gaps. After the first review, ask: "What behavior changed that is not covered by tests?"

This is especially useful for UI states, error handling, redirects, permissions, and date/time behavior.

Copyable prompts

Strict Codex code review

Review this change as a senior engineer. Findings first. Prioritize bugs, regressions, missing tests, security/privacy issues, accessibility, and unclear behavior. Use file references. After findings, list open questions, then a short summary. If there are no serious issues, say that clearly and name residual risk.

Codex test gap review

Look only for missing or weak tests in this change. What behavior changed? What edge cases are not covered? Which tests would give the most confidence? Keep it concrete and avoid generic testing advice.

Codex review-to-patch prompt

Fix only these agreed review findings: [FINDINGS]. Keep the patch minimal. Do not refactor unrelated code. Run [CHECKS] and summarize exactly what changed.

Related Power of AI pages

Codex Best Practices: Set up better Codex sessions before review.
Claude Code vs Codex: Choose which agent should review what.
AI Coding Agents: Understand agent workflows broadly.

Sources and official references

Related Power of AI pages

Keep reading with AI Finder, Prompt Studio, ChatGPT vs Claude vs Gemini, the AI glossary, and Which AI Should You Use?.