Automate actions with Hooks

🎯Goal. Run your own shell commands automatically before or after Claude's actions — formatting, linting, or filtering output.

1. 1Hooks run a shell command around Claude Code events. Common uses: auto-format after every file edit, run lint before a commit, or grep a huge log down to just the errors before Claude reads it.
2. 2Configure them in settings.json — e.g. a PreToolUse hook with a Bash matcher that filters test output to show only failures, cutting context from tens of thousands of tokens to hundreds.
3. 3Hooks make behavior deterministic where you need it — the command always runs; you're not relying on Claude to remember.

✓You'll see. Your formatter or linter firing automatically on every edit, with no reminder needed.

💳Cost. A pre-processing hook (e.g. grepping a log for ERROR) can slash the context Claude reads, directly lowering token cost.

💡Takeaway. Hooks turn "please remember to lint" into a guarantee — a shell command that always runs at the right moment.