create-commit-message

name	create-commit-message
description	Generate a Conventional Commit message from staged git changes when the user asks to write a commit message, create a commit, or format a commit
author	chalk
version	1.0.0
metadata-version	3
allowed-tools	Read, Glob, Grep, Bash
argument-hint	[optional: additional context about why this change was made]
read-only	false
destructive	false
idempotent	false
open-world	true
user-invocable	true
tags	git, vcs, automation

Create Commit Message

Overview

Generate a precise, Conventional Commits-formatted commit message by analyzing the staged git diff. The message classifies the change type, infers the scope from changed files, writes a clear subject line under 72 characters, and adds a body for complex changes explaining why the change was made.

Workflow

1. Read project context -- Check for .chalk/docs/engineering/ files, especially:

   • Commit message conventions or contributing guides
   • Any custom commit types or scopes used by this project
   • Check for a commitlint.config.js or similar configuration that defines allowed types and scopes
   • If custom conventions exist, follow those instead of the defaults below

2. Get the staged diff -- Run:

   • git diff --cached --stat for a high-level overview of changed files
   • git diff --cached for the full diff content
   • git status to check for unstaged changes the user may have forgotten to stage
   • If nothing is staged, inform the user and suggest staging commands

3. Classify the change type -- Analyze the diff content (not just file names) to determine the primary type:

   Type	When to Use
   feat	New functionality visible to users or consumers of the module
   fix	Corrects a bug -- behavior was wrong, now it is right
   refactor	Code restructuring with no behavior change
   docs	Documentation only -- README, JSDoc, comments, guides
   test	Adding or updating tests with no production code change
   chore	Maintenance tasks: dependency updates, config changes, tooling
   perf	Performance improvement with no functional change
   ci	CI/CD pipeline changes (GitHub Actions, CircleCI, etc.)
   build	Build system changes (webpack, tsconfig, Dockerfile, etc.)
   style	Code formatting only -- whitespace, semicolons, no logic change
   revert	Reverts a previous commit

   Decision rules:

   • If the diff includes both a feature and tests for that feature, the type is feat (tests are part of the feature)
   • If the diff includes both a fix and a test that reproduces the bug, the type is fix
   • If you are genuinely unsure, ask the user -- do not guess

4. Infer the scope -- Determine the scope from the changed files:

   • If all changes are in src/auth/ or lib/auth/, scope is auth
   • If all changes are in components/Button/, scope is button
   • If changes span multiple directories but share a domain, use the domain name
   • If changes are truly cross-cutting, omit the scope
   • Match existing scope conventions -- run git log --oneline -50 and extract scopes from prior commits
   • Scope should be lowercase, typically one word

5. Write the subject line -- Format: type(scope): description

   • Total length: 72 characters maximum (including type and scope)
   • Start with a lowercase imperative verb: "add", "fix", "remove", "update", "refactor"
   • Do not end with a period
   • Describe the what concisely -- the body explains why
   • Be specific: "fix null pointer in user lookup" not "fix bug"

6. Write the body (if needed) -- Add a body separated by a blank line when:

   • The change is not obvious from the subject line alone
   • There is important context about why this change was made
   • The approach was non-obvious and the reasoning should be documented
   • The body should explain motivation, not repeat the diff
   • Wrap lines at 72 characters

7. Write the footer (if needed) -- Add footers for:

   • Breaking changes: BREAKING CHANGE: <description of what breaks and migration path>
   • Issue references: Fixes #123 or Closes #456 or Refs #789
   • Co-authors: Co-authored-by: Name <email>

8. Present the commit message -- Output the complete commit message in a code block. Also output the git command to create the commit so the user can copy-paste it.

Commit Message Format

type(scope): subject line under 72 chars

Optional body explaining WHY this change was made, not WHAT changed
(the diff shows what changed). Wrap at 72 characters.

Motivation: explain the problem or opportunity.
Approach: explain why this approach was chosen over alternatives.

BREAKING CHANGE: description of what breaks and how to migrate

Fixes #123

Examples

Simple Feature

feat(auth): add password reset via email link

Bug Fix with Context

fix(checkout): prevent double-charge on retry after timeout

When a payment request timed out, the retry logic did not check whether
the original charge succeeded. This caused double-charges for ~0.3% of
transactions. Now we query the payment provider for existing charges
before retrying.

Fixes #892

Refactor

refactor(api): extract validation middleware from route handlers

Validation logic was duplicated across 12 route handlers with slight
variations. Extracted into a shared middleware that takes a Zod schema,
reducing duplication and ensuring consistent error responses.

Breaking Change

feat(api): require API key for all public endpoints

Previously, rate limiting on public endpoints relied on IP-based
throttling, which was easily circumvented. All public endpoints now
require an API key passed via the X-API-Key header.

BREAKING CHANGE: All API requests must include an X-API-Key header.
Existing clients need to register for an API key at /developer/keys
before upgrading.

Refs #1045

Chore

chore(deps): upgrade express from 4.18 to 4.19

Includes security patch for CVE-2024-XXXXX (prototype pollution in
query parser). No breaking changes per the changelog.

Subject Line Rules

Rule	Good	Bad
Imperative mood	add user search	added user search
Lowercase start	fix timeout	Fix timeout
No period	update readme	update readme.
Specific	fix null pointer in user lookup	fix bug
Under 72 chars	feat(auth): add OAuth2 PKCE flow	feat(authentication-service): add the OAuth2 PKCE flow for single-page applications
Describes what, not how	add retry logic for payments	add try-catch block around payment call

Type Classification Decision Tree

Is there new user-visible functionality?
├── Yes → feat
└── No
    Was behavior incorrect before?
    ├── Yes → fix
    └── No
        Did only tests change?
        ├── Yes → test
        └── No
            Did only docs/comments change?
            ├── Yes → docs
            └── No
                Did behavior change?
                ├── No (same behavior, different structure) → refactor
                └── No (same behavior, faster) → perf
                    Is it CI/CD config?
                    ├── Yes → ci
                    └── Is it build config?
                        ├── Yes → build
                        └── Is it formatting only?
                            ├── Yes → style
                            └── chore

Anti-patterns

• Meaningless subjects -- "fix stuff", "WIP", "update", "changes", "misc" communicate nothing. Every commit message must describe a specific change. If you cannot describe it specifically, the commit is doing too many things -- split it.
• Scope that does not match the changed area -- fix(auth): update button color is wrong. The scope must reflect the area of code that actually changed. If the scope does not match, either the scope is wrong or the files are in the wrong directory.
• Body that repeats the diff -- "Changed line 45 from X to Y" is useless as a body. The body explains why -- the what is in the diff. If the subject line fully explains the change, omit the body entirely.
• Multiple unrelated changes in one commit -- If you cannot describe the commit in one subject line, it should be multiple commits. A commit that "add search and fix login and update deps" is three commits.
• Missing BREAKING CHANGE footer -- If the change breaks backwards compatibility for any consumer, the BREAKING CHANGE: footer is mandatory. Omitting it means consumers get surprised at deploy time.
• Past tense -- "fixed", "added", "updated" instead of "fix", "add", "update". Conventional Commits uses the imperative mood because commit messages complete the sentence "This commit will...".
• Overly broad scope -- feat(app): ... or fix(src): ... are not useful scopes. The scope should identify the module, component, or domain -- not the top-level directory.
• Commit message longer than the change -- A one-line config change does not need a 10-line body. Scale the message to the complexity of the change.