Code Review

Use this skill when performing code reviews or pull request reviews.

Base Branch Determination

Before reviewing, you must determine the correct base branch. Use these methods in order of reliability:

Method 1: Check for Associated PR/MR

If the branch has an open pull request or merge request, use the PR's target:

# GitHub
gh pr view --json baseRefName --jq '.baseRefName' 2>/dev/null

# GitLab
glab mr view --output json 2>/dev/null | jq -r '.target_branch'

Method 2: Check Upstream Tracking

If the branch tracks a remote branch that itself branched from somewhere:

git config --get branch.<branch-name>.merge

Method 3: Find Merge Base with Default Branches

Attempt to find a common ancestor with likely default branches:

# Check if main or master exists and find merge-base
for base in main master develop; do
  if git rev-parse --verify "origin/$base" >/dev/null 2>&1; then
    merge_base=$(git merge-base "origin/$base" HEAD)
    echo "$base: $merge_base"
  fi
done

This helps identify which branch HEAD diverged from, but does not guarantee the intent of the branch author.

When Base Cannot Be Determined

If none of the above methods provide a clear answer, do not assume. Ask the user:

I cannot determine which branch this was based off. What branch should I use as the base for comparison? Common options include main, master, or develop.

Proceeding with an incorrect base will cause the review to include out-of-scope changes or miss in-scope changes.

Scope Determination

Focus only on commits that are contained within the branch being reviewed. Use git diff <base-branch>...HEAD to determine what is in scope.

# List commits on the branch
git log --oneline <base-branch>..HEAD

# Get the full diff for review
git diff <base-branch>...HEAD

# Get diff for a specific file
git diff <base-branch>...HEAD -- <file>

Pre-existing Code

If a bug, convention violation, or inconsistent naming existed in code before the branch, do not treat it as a problem in the review. This includes cases where refactored code retains a pre-existing type name, variable name, or pattern that does not match current conventions.

Only evaluate the changes introduced by the branch.

Convention Compliance

All new logic, patterns, and naming introduced by the branch should follow the project's established conventions. Pre-existing code that appears in the diff due to refactoring is exempt from this requirement.

If reviewing TypeScript code, consider loading the typescript-conventions skill for detailed guidance on type patterns, naming, and idioms.

Delegating to Sub-agents

When delegating file review to sub-agents, provide the output of git diff <base-branch>...HEAD -- <file> rather than the full file contents.

Sub-agents that receive full files cannot distinguish branch changes from pre-existing code and will flag out-of-scope issues.

If full files must be provided for context, explicitly instruct the sub-agent which line ranges were modified by the branch and that only those ranges are in scope.

Test Coverage Philosophy

Do not request additional test coverage for functionality provided by external libraries. Focus test coverage requests on:

• Business logic and domain-specific validation
• Integration points between components
• Error handling paths and edge cases
• Custom algorithms and data transformations

Trust well-maintained libraries to do their job. If a library's behavior needs testing, that suggests reconsidering whether to use that library.

Review Checklist

1. Determine the base branch using the methods in "Base Branch Determination"
2. Run git log --oneline <base>..HEAD to understand the scope
3. Run git diff <base>...HEAD --stat to see which files changed
4. Review each changed file, focusing only on lines modified by the branch
5. Check that new code follows project conventions
6. Summarize findings with specific file:line references