VelimirMueller Write Commit Messages
The diff already records what changed; the message carries what the diff cannot — the motivation, the shape, the approach. Subject in the repository's own convention; body in three labeled groups — Why, What, How — every line derived from the diff.
1. Audit — the diff and the house convention
git diff --staged # or: git show <commit>, for an existing message
git log --oneline -15
Read the actual diff: the body will be derived from it, never from memory of what was
intended. From the log, detect the subject convention — conventional commits
(feat(scope): …), gitmoji, or plain imperative — and match it; default to conventional
commits only when no convention is detectable. Change nothing yet.
2. Decide
- The diff mixes concerns (a feature plus an unrelated fix) → propose the split before writing anything: one concern per commit, one message each.
- A commit exists and only its message is wrong → amend rather than stack a fixup:
git commit --amend. Safe only while the commit is unpushed and unshared — rewriting published history breaks everyone who pulled it. Already pushed → never amend; when the message is still wanted (a squash target, the spine of a PR description), draft it without touching history. - The message already conforms (subject in convention, the three groups present) → report "already in place" and exit. A second run writes nothing.
3. Draft the subject
In the detected convention, imperative mood, aim ≤72 characters, the one concern named.
Test: "applying this commit will " reads as a sentence — the description after
any type(scope): prefix is what must parse (./commit-patterns.md for the discipline).
4. Draft the body — Why, What, How
Three labeled bullet groups, each grounded in the step-1 diff:
Why:
- the problem or motivation — the one thing the diff cannot show
What:
- the change at a glance: surface, files, behavior
How:
- the approach taken and its trade-offs
Every bullet concrete — a path, a behavior, a named mechanism, a number — and project
jargon glossed on first use. What separates concrete from filler: ./commit-patterns.md.
Keep the trailers the house convention carries (Co-Authored-By:, Signed-off-by:)
after the three groups — they are part of what the step-1 audit detects.
5. Self-check — the audience contract
Run the three tests from ../_shared/audience.md: a junior can follow the message
without tribal knowledge, a senior can verify each bullet against the diff, a CTO gets
outcome and risk from the labels and first lines alone. Any unexplained jargon or
unverifiable claim → revise before showing it.
6. Verify
Show the final message for approval before committing; after committing, confirm:
git log -1 --format=%B
The printed message matches what was approved: subject in the repo's convention, the three labeled groups present.
References
- ./commit-patterns.md — the rules with rationale, the unguided baseline as anti-example, and a worked rewrite of a real commit.
- ../_shared/audience.md — the junior-to-CTO contract step 5 checks against.
- ../write-pull-requests/SKILL.md — the same Why/What/How spine at PR scale; on squash-merge, the PR description becomes this commit's message.