name: general-codereview description: Perform thorough code reviews following Google's 5-step methodology. Use when reviewing pull requests, change lists, or any code changes to ensure quality, correctness, and maintainability. license: MIT metadata: author: Zainan Victor Zhou version: "1.0" origin: "Based on 5 steps to perform code reviews at Google (2013)"

General Code Review Skill

A comprehensive code review methodology based on Google's engineering practices. Follow these 5 steps to perform effective and thorough code reviews.

Step 1: Pre-screen

Before diving into the code, perform a quick pre-screening:

Check Size

• Reasonable size: A change list of ~300 lines of code is typically reasonable
• Too large: Larger CLs should be strongly discouraged unless necessary
  • Leave a comment asking if the CL can be broken down into smaller, logically complete parts
  • Ask for the reason if breaking down is not possible
• Small is OK: Even single-line changes are fine as long as they are logically complete

Verify You're the Right Reviewer

Ask yourself:

• Am I familiar enough with this code area?
• Do I understand the language, environment, and context?
• Is there someone better suited to review this?

If you're not the ideal reviewer but no one else is available, prepare to quickly learn about the unfamiliar aspects.

Step 2: Understand

After pre-screening, focus on understanding the change from the author's perspective.

Purpose

Ask: "Do I know the overall purpose of this CL?"

• The purpose should be clearly stated in the CL description
• If unclear, request clarification
• Even self-explanatory code needs a clear description for future maintainers
• Remember: even the author may need to refer back to the description later

Workflow Context

Ask: "Was I expecting this CL? Does it match my expectations?"

Consider:

• Is this CL part of a larger project or design doc?
• Does it align with the task distribution and design documentation?
• Are there dependencies mentioned?
  • Other changes that need to happen before this CL can function
  • Other CLs that are blocked by this change

Design Decisions

Verify that important design decisions are:

• Documented in the code description
• Explained with rationale when non-obvious

Step 3: Verify

Now verify the implementation matches the stated intent.

Code-Description Alignment

• Verify the code does what the description says
• Flag any discrepancies between stated purpose and actual implementation

Test Coverage

Verify relevant tests exist for:

Step 4: Optimize

Look for opportunities to improve the code's efficiency and maintainability.

Logic Optimization

• Can the algorithm be simplified?
• Are there unnecessary computations?
• Is the control flow optimal?

Library Usage

• Is the best library being used for this task?
• Are there more appropriate or efficient alternatives?
• Is the library being used correctly and efficiently?

Step 5: Check Style

Final pass for code style and conventions.

Style Checklist

• Follows project/team coding standards
• Consistent naming conventions
• Proper formatting and indentation
• Clear and helpful comments
• No dead code or debugging artifacts

Quick Reference Checklist

□ Pre-screen
  □ Size reasonable (~300 lines)?
  □ Am I the right reviewer?

□ Understand
  □ Purpose clear in description?
  □ Expected in current workflow?
  □ Design decisions documented?

□ Verify
  □ Code matches description?
  □ Tests cover design decisions?
  □ Tests cover defaults and edge cases?

□ Optimize
  □ Logic optimizable?
  □ Library choices optimal?

□ Check
  □ Style guidelines followed?

Acknowledgment: This methodology is based on reflections from working at Google, with thanks to mentors and teammates who helped improve these code review skills.