Git Commit Writer

Git Commit Writer

What this skill does

This skill directs the agent to read a git diff (or a plain description of changes) and produce a well-formed commit message following the Conventional Commits specification. It chooses the right type (feat, fix, chore, docs, refactor, test, style, perf, ci), picks an appropriate scope, writes a concise subject line, and — when the change is large enough to warrant it — adds a descriptive body.

Use this when you want consistent, meaningful commit history without having to remember the format every time.

How to use

Claude Code / Cline

Copy this file to .agents/skills/git-commit-writer/SKILL.md in your project root.

Then ask the agent:

• "Write a commit message for my staged changes using the Git Commit Writer skill."
• "Here's a diff. Use the Git Commit Writer skill to produce a commit message."

For Claude Code, you can also run git diff --staged first and paste the output into the chat.

Cursor

Add the contents of the "Prompt / Instructions" section below to your .cursorrules file, or paste it into the Cursor AI pane before asking for a commit message.

Codex

Paste the diff into the Codex chat along with the instructions from the section below. Codex works best when you include the full diff rather than a summary.

The Prompt / Instructions for the Agent

When asked to write a commit message, follow these steps:

1. Read the diff. If not provided, ask for git diff --staged output. Understand every file changed.

2. Determine the commit type using these rules:

   • feat — a new feature or behavior visible to users or callers
   • fix — a bug fix
   • refactor — code restructuring with no behavior change
   • perf — performance improvement
   • test — adding or fixing tests
   • docs — documentation only (README, comments, etc.)
   • style — formatting, whitespace, lint (no logic change)
   • chore — build scripts, dependencies, tooling
   • ci — CI/CD pipeline changes

3. Choose a scope (optional but recommended). The scope is the part of the codebase most affected, in lowercase: auth, api, ui, db, parser, etc. Use the folder name or module name if unsure.

4. Write the subject line (first line of the commit):

   • Format: type(scope): short description
   • Max 72 characters
   • Use the imperative mood: "add", "fix", "remove" — not "added", "fixing", "removes"
   • Do not capitalize the first word after the colon
   • Do not end with a period

5. Write the body if the change needs explanation:

   • Leave a blank line between subject and body
   • Explain why the change was made, not what (the diff shows what)
   • Wrap lines at 72 characters
   • Use bullet points for multiple distinct changes

6. Add a footer if applicable:

   • Breaking changes: BREAKING CHANGE: description
   • Issue references: Closes #123 or Fixes #456

7. Output format:

type(scope): short imperative description

Optional body explaining the why behind the change.
Can be multiple paragraphs. Wrap at 72 chars.

Optional footer: Closes #123

If the diff contains multiple unrelated changes, flag this and suggest splitting into separate commits.

Example

Input to Agent:

"Here's my staged diff. Write a commit message using the Git Commit Writer skill.

diff --git a/server/auth.ts b/server/auth.ts
index 3a1b2c..9f4e5d 100644
--- a/server/auth.ts
+++ b/server/auth.ts
@@ -42,6 +42,12 @@ export async function login(email: string, password: string) {
   const user = await db.users.findOne({ email });
   if (!user) throw new AuthError('User not found');
+
+  if (user.lockedUntil && user.lockedUntil > new Date()) {
+    throw new AuthError('Account is temporarily locked. Try again later.');
+  }
+
   const valid = await bcrypt.compare(password, user.passwordHash);
   if (!valid) {
+    await incrementFailedAttempts(user.id);
     throw new AuthError('Invalid password');
   }
```"

Output from Agent:

fix(auth): lock accounts after repeated failed login attempts

Adds a check for the `lockedUntil` field before attempting password
comparison. Also increments a failed-attempt counter on each bad
password so the locking mechanism has data to act on.

Notes

• If you paste a large diff with changes spanning many files and concerns, the agent may suggest splitting it. That is intentional behavior — large atomic commits make history harder to read.
• The skill does not run git commit automatically. It only produces the message text for you to review and use.
• For monorepos, use the package or workspace name as the scope (e.g., feat(api-gateway): ...).