Skill: commit-history-audit

Purpose

Catch commit hygiene problems before a PR reviewer does. Writing a good commit is covered by commit-message; this skill audits what's already on the branch — the full history from the point it diverged from the base branch — and produces a compliance report with specific remediation steps.

Convention detection is self-calibrating: the skill reads the repo's own commit history to determine what standards are in use before checking anything. It never imposes Conventional Commits on a repo that doesn't already use it.

Trigger phrases

• "audit my commits"
• "check commit history before PR"
• "are my commits clean"
• "commit-history-audit"
• "review my branch commits"
• "check my git history"

Steps

1. Determine the base branch and divergence point

# Identify the base branch (try common names in order)
git remote show origin 2>/dev/null | grep "HEAD branch" | awk '{print $NF}'
# Fallback: check for main, master, develop
git branch -r | grep -E "origin/(main|master|develop)" | head -1

# Find commits on this branch not on the base branch
git log --oneline main..HEAD        # replace 'main' with the detected base branch

If the branch has no divergence (is at HEAD of base), say so and stop — nothing to audit.

2. Collect full commit data

git log main..HEAD \
  --pretty=format:"%H|%s|%an|%ae|%ai|%P" \
  --no-merges

Also collect any merge commits separately:

git log main..HEAD --merges --oneline

3. Detect the repo's commit convention

Before checking anything, read the base branch history to understand what this repo actually does:

git log origin/main -50 --pretty=format:"%s" 2>/dev/null | head -50

Classify the repo into one of three modes:

Record the detected mode and state it at the top of the audit report.

4. Audit each commit against these rules

For every commit (excluding merge commits for rules 1–4, analysing merges in rule 5):

#### Rule 1 — Commit convention compliance (conditional on detected mode)

Conventional Commits mode only:

Subject must match: ^(feat|fix|refactor|docs|test|chore|perf|style|ci|build|revert)(\(.+\))?: .+

Flag: subject does not match — label [NO-CONVENTION]

Ticket-prefixed mode only:

Subject must start with a ticket reference matching the detected pattern (e.g. PROJ-123, #42).

Flag: subject has no ticket reference — label [NO-TICKET]

Free-form mode: Rule 1 does not apply. Skip it.

#### Rule 2 — Subject line length

Subject ≤ 72 characters. Applies in all modes.

Flag: exceeds limit — label [TOO-LONG] with current character count

#### Rule 3 — Imperative mood (heuristic)

Subject must not start with a past-tense or gerund verb. Applies in all modes.

Common violations: starts with "added", "adding", "fixed", "fixing", "updated", "updating", "changed", "changing", "removed", "removing"

Flag: detected past/gerund — label [PAST-TENSE]

#### Rule 4 — WIP / draft commits

Subject contains: wip, WIP, fixup!, squash!, temp, tmp, do not merge, dnm. Applies in all modes.

Flag — label [WIP]

#### Rule 5 — Merge commits (squash/rebase repos only)

Check the base branch merge style:

git log origin/main -20 --merges --oneline

If base branch has zero merge commits → repo uses squash or rebase strategy.

Flag any merge commit on the branch — label [MERGE-COMMIT]. Skip this rule if the base branch itself contains merge commits (the repo allows them).

#### Rule 6 — Single-purpose signal (advisory only, all modes)

If the branch touches clearly unrelated concerns across commits (e.g. UI changes mixed with database migrations), note this as a signal for the reviewer. Not a violation — never produces a flag in the table.

5. Produce the audit report

Output a structured report in this format:

## Commit History Audit — <branch-name>

Convention mode detected: Conventional Commits | Ticket-prefixed (PROJ-NNN) | Free-form
Base branch: <main|master|develop>
Commits audited: <N>
Merge commits found: <N>

### Results

| # | Short SHA | Subject | Issues |
|---|-----------|---------|--------|
| 1 | abc1234   | feat: add login page | ✅ |
| 2 | def5678   | Added user model | [NO-CONVENTION] [PAST-TENSE] |
| 3 | ghi9012   | wip fixes | [WIP] [NO-CONVENTION] |

### Violations Summary

**[NO-CONVENTION]** — 2 commits
**[PAST-TENSE]** — 1 commit
**[WIP]** — 1 commit

### Compliance Score

X / N commits clean  →  <PASS | NEEDS CLEANUP>

Pass threshold: all commits must be violation-free for a PASS.

### Remediation

For each violation, provide the specific fix:

**def5678 — "Added user model"**
Suggested rewrite: `feat(auth): add user model`
To amend: `git rebase -i main` and reword this commit.

**ghi9012 — "wip fixes"**
This commit should be squashed into its predecessor or given a meaningful message.
To squash: `git rebase -i main` and mark this commit `squash` or `fixup`.

6. Offer next steps

After the report, ask:

"Would you like me to generate the interactive rebase commands to fix these, or open the PR as-is with a note about the history?"

Do not run git rebase automatically — that is a destructive operation requiring user confirmation.

Output

• A markdown audit table with per-commit flags
• A violations summary with counts
• A compliance score (PASS / NEEDS CLEANUP)
• Specific remediation steps for each failing commit

Notes

• If the branch has more than 50 commits, warn the user: "This is a large branch. Auditing the last 50 commits — pass --all to audit further back."
• Commits by bots (email contains [bot] or noreply) are excluded from the audit.
• This skill audits; it does not rewrite. All git history changes require explicit user action.
• Works alongside pre-commit-check (which audits staged changes before a single commit) and pr-summary (which creates the PR after history is clean).