Agent skill

commit-message-generator

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Install this agent skill to your Project

npx add-skill https://github.com/brendendurham/claude-code-config/tree/main/skills/commit-message-generator

SKILL.md

Commit Message Generator Skill

Generate well-structured conventional commit messages by analyzing git diffs.

When to Use

  • User asks to "generate commit message" or "write commit"
  • User wants help describing their changes
  • User asks for conventional commit format

Conventional Commit Format

<type>(<scope>): <subject>

<body>

<footer>

Type Prefixes

Type Description Example
feat New feature feat(auth): add OAuth2 login
fix Bug fix fix(api): handle null response
docs Documentation only docs(readme): update install steps
style Formatting, no code change style(lint): fix indentation
refactor Code change, no feature/fix refactor(utils): simplify date parsing
perf Performance improvement perf(db): add query indexing
test Adding/fixing tests test(auth): add login unit tests
build Build system changes build(webpack): update config
ci CI configuration ci(github): add deploy workflow
chore Maintenance tasks chore(deps): update dependencies
revert Revert previous commit revert: undo feature X

Scope Detection

Analyze the changed files to determine scope:

  1. Directory-based: src/components/Button.tsx -> scope: button or components
  2. Feature-based: Changes to auth files -> scope: auth
  3. Layer-based: API changes -> scope: api
  4. Multiple scopes: Use comma separation (auth,api) or omit scope for broad changes

Common scope patterns:

  • api, ui, db, auth, config
  • Component/module names: navbar, checkout, user
  • Layer names: controller, service, model

Generation Process

Step 1: Analyze the Diff

bash
# Get staged changes
git diff --cached

# Or get all uncommitted changes
git diff HEAD

# Get file names only for quick overview
git diff --cached --name-only

Step 2: Categorize Changes

  1. Identify primary intent: Is this a feature, fix, refactor, etc.?
  2. Find the scope: What area of the codebase is affected?
  3. Note breaking changes: Any backward incompatible changes?
  4. Check for related issues: PR numbers, issue references

Step 3: Craft the Message

Subject Line Rules

  • Use imperative mood ("add" not "added" or "adds")
  • No period at the end
  • Max 50 characters (hard limit: 72)
  • Lowercase after type prefix
  • Be specific but concise

Good examples:

  • feat(cart): add quantity validation on checkout
  • fix(api): handle timeout on slow connections
  • refactor(auth): extract token logic to service

Bad examples:

  • feat: updated stuff (vague)
  • Fixed the bug. (wrong format, past tense, period)
  • feat(authentication-module): implemented new OAuth2 authentication flow (too long)

Body Guidelines

  • Wrap at 72 characters
  • Explain WHAT and WHY, not HOW
  • Leave blank line after subject
  • Use bullet points for multiple changes

Footer Guidelines

  • Reference issues: Fixes #123, Closes #456
  • Note breaking changes: BREAKING CHANGE: description
  • Co-authors: Co-authored-by: Name <email>

Output Format

Provide the commit message in a code block:

<type>(<scope>): <subject>

<body explaining the change>

<footer with references>

Then explain your reasoning:

Analysis:

  • Primary change type: {type}
  • Detected scope: {scope}
  • Files affected: {count}
  • Breaking changes: Yes/No

Examples

Example 1: Simple Feature

Diff shows: New validateEmail function added to utils/validation.js

feat(validation): add email format validation utility

Add validateEmail function that checks for proper email format
using RFC 5322 compliant regex pattern. Returns boolean result.

- Supports international domains
- Handles edge cases like plus addressing

Example 2: Bug Fix with Issue Reference

Diff shows: Fix for null pointer in UserService.getProfile()

fix(user): handle missing profile data gracefully

Return empty profile object instead of throwing when user
profile data is null. This prevents crashes on new accounts
that haven't completed onboarding.

Fixes #234

Example 3: Breaking Change

Diff shows: Changed API response format in api/v2/users

feat(api)!: restructure user response payload

Flatten nested user object and rename fields for consistency
with API design guidelines.

Changes:
- user.profile.name -> user.name
- user.profile.email -> user.email
- user.settings.* -> user.preferences.*

BREAKING CHANGE: User API response structure changed.
Clients must update to handle new flat structure.
Migration guide: docs/migrations/user-api-v2.md

Closes #567

Example 4: Multiple Small Changes

Diff shows: Various small updates across files

chore: update dependencies and fix linting

- Bump eslint to v8.50.0
- Update prettier config for new rules
- Fix auto-fixable lint warnings
- Remove unused imports in 3 files

Tips

  1. One commit, one purpose: If you struggle to write a concise message, the commit may be too large
  2. Think about git log: Will this message make sense in 6 months?
  3. Consider reviewers: The message is for humans, not just history
  4. Use present tense: "add feature" not "added feature"
  5. Be atomic: Each commit should be a complete, working change

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