Reviewing Code

Code Review

Use this skill when the user asks for a code review, feedback on their code, or to check code quality.

Steps

1. Understand the change — read the files or diff to understand what the code is supposed to do. Identify the scope (new feature, bug fix, refactor).

2. Check correctness

   • Does the code handle edge cases (empty input, null, zero, negative numbers)?
   • Are error states handled (try/catch, error boundaries, fallback UI)?
   • Does async code handle race conditions, cancellation, and timeouts?
   • Are there off-by-one errors in loops or array access?

3. Check maintainability

   • Are functions focused on a single responsibility?
   • Are variable and function names descriptive?
   • Is there unnecessary duplication that should be extracted?
   • Are magic numbers replaced with named constants?
   • Is the code complexity reasonable (deeply nested conditionals, long functions)?

4. Check performance

   • Are there N+1 query patterns in database access?
   • Are expensive computations or API calls happening in render loops?
   • Are large lists missing virtualization or pagination?
   • Are there missing indexes for common database queries?
   • Is memoization used appropriately (not over-applied)?

5. Check type safety (TypeScript projects)

   • Are there any types that should be narrowed?
   • Are function return types explicit for public APIs?
   • Are union types handled exhaustively?

6. Check testing

   • Are there tests for the new/changed code?
   • Do tests cover the happy path AND error cases?
   • Are tests isolated (no shared mutable state)?

7. Provide feedback — organize findings by severity:

   • Must fix: bugs, security issues, data loss risks
   • Should fix: performance issues, maintainability concerns
   • Nit: style preferences, minor suggestions

   For each finding, include the file, line, the issue, and a suggested fix.

Notes

• Be constructive — explain why something is a problem, not just that it is.
• Acknowledge what's done well, not just what needs fixing.
• Don't bikeshed on style issues that a linter/formatter should handle.