thoughtbot Atomic Commits
Work in small, focused increments. Every commit should be atomic. Every PR should be reviewable in one sitting.
Atomic Commit Criteria
Every commit must:
- Pass CI — tests, linter, build all green
- Be deployable — application is in a valid state
- Introduce no dead code — no unreachable code, unused imports, or half-wired features
One Commit, One Type of Work
- Refactor — restructure code without changing behavior
- Feature — the behavior change itself
- Cleanup — remove old code, update docs
If the commit message needs "and", split it.
PR Size
Target ~200 lines per PR. If larger, find a seam — ship refactor and feature as separate PRs, each independently mergeable and deployable.
Agent Behavior
- Plan atomic steps before coding: refactors, then features, then cleanup.
- Commit after each atomic step — don't accumulate.
- Stage selectively (
git add --patchor specific files). - When branch diff nears 200 lines, open a PR and continue in a follow-up.
Hook
This skill includes a PostToolUse hook (hooks/check-diff-size.sh) that monitors diff size after Edit/Write operations and nudges when it's time to commit or open a PR.