Lefthook

Lefthook

Create or update Lefthook configuration with exact option names, practical defaults, and clear debugging steps. Explain the tool briefly, then produce a working config for the current repository.

Use this skill when the task mentions:

• lefthook.yml, .lefthook.yml, .config/lefthook.yml, lefthook-local.yml, or another lefthook-local.* file
• Git hooks such as pre-commit, commit-msg, pre-push, post-merge, or post-checkout
• lefthook install, lefthook run, lefthook dump, or lefthook validate
• choosing between commands, jobs, and scripts
• placeholders such as {staged_files}, {push_files}, {all_files}, {files}, or {1}
• hook bugs such as commands not running, wrong files matching, fixed files not restaged, or local-only wrappers leaking into shared config

Non-Negotiables

1. Inspect the repository before writing config. Reuse the existing config filename and format if one already exists.
2. Match hook commands to the repo's real toolchain. Reuse existing package manager commands, scripts, and linters instead of inventing wrappers.
3. Choose the simplest structure that fits. Use commands by default, jobs for ordering or grouping, and scripts only for executable hook files.
4. Use placeholders and filters that match the hook type. pre-commit usually wants {staged_files}, pre-push usually wants {push_files}, and commit-msg usually wants {1}.
5. Add stage_fixed: true only for commands that rewrite tracked files and should re-stage them.
6. Put local-only skips, Docker wrappers, and private overrides in lefthook-local.*, not in the shared team config.
7. When debugging or reviewing, use lefthook validate, lefthook dump, and lefthook run <hook> before guessing.

Start Here

Inspect the repository before writing anything.

• Look for existing config files first: lefthook.yml, .lefthook.yml, .config/lefthook.yml, lefthook.yaml, lefthook.toml, lefthook.json, lefthook.jsonc, and matching lefthook-local.* overrides.
• Preserve the existing format and naming if a config already exists.
• Prefer YAML lefthook.yml for new setups unless the repo already standardizes on TOML, JSON, or JSONC.
• Read package manager files, script directories, and CI or lint tooling before proposing hook commands.
• Keep one main format per project. Do not introduce a second main Lefthook config format.

Author Configs

Choose the simplest structure that fits the workflow.

• Use commands for the default case: straightforward named tasks such as linting, formatting, tests, or commit message checks.
• Use jobs when order, grouping, parallel, piped, mixed run and script entries, or merge-friendly named jobs matter.
• Use scripts only when the repository already uses executable files under source_dir/<hook>/ or when the user explicitly wants file-based scripts.
• Prefer hook names that match real Git hooks such as pre-commit, commit-msg, and pre-push. It is also valid to define custom task groups and run them through lefthook run <name>.
• Keep commands local to the repo toolchain. Reuse existing npm, pnpm, yarn, bun, go, bundle, uv, or shell commands instead of inventing new wrappers.
• Use file templates deliberately: {staged_files} for pre-commit, {push_files} for pre-push, {all_files} for whole-repo checks, {files} when a custom files: command is defined, {cmd} for local wrapping, and {1} for hook arguments such as commit-msg.
• Add stage_fixed: true only when the command actually rewrites tracked files and should re-stage them.
• Use glob, exclude, file_types, and root to keep commands narrow and fast.
• Reach for lefthook-local.* when the user wants local-only skips, Docker wrappers, or private overrides that should not change the shared team config.

Integrated example for a JS or TS repo that already uses ESLint, Prettier, and Commitlint:

pre-commit:
  commands:
    eslint:
      glob: "*.{js,jsx,ts,tsx}"
      run: pnpm eslint --fix {staged_files}
      stage_fixed: true
    prettier:
      glob: "*.{js,jsx,ts,tsx,json,md,yml,yaml}"
      run: pnpm prettier --write {staged_files}
      stage_fixed: true

commit-msg:
  commands:
    commitlint:
      run: pnpm commitlint --edit {1}

Why this shape:

• commands is enough because each task is independent.
• pre-commit uses {staged_files} because the checks should scope to the staged set.
• commit-msg uses {1} because Git passes the commit message file path as the first hook argument.
• Both formatters set stage_fixed: true because they rewrite tracked files.

Read overview.md for install and command flow, config-model.md for structure and merge behavior, patterns.md for common recipes, best-practices.md when the user asks for battle-tested guidance, and schema-cheatsheet.md for exact keys.

Explain And Debug

Explain Lefthook in terms of repository behavior, not marketing.

• Describe it as a Git hook manager that reads config on each run and executes repo-defined commands or scripts.
• Mention that lefthook install installs Git hook entrypoints and creates an empty config if none exists.
• Mention that config changes do not require reinstall in normal cases because hooks read config each time they run.
• Use lefthook validate to check configuration validity.
• Use lefthook dump to inspect the effective merged config after extends, remotes, and lefthook-local.*.
• Use lefthook run <hook> with --all-files, --file, --job, or --tag to reproduce hook behavior outside git commit or git push.
• Explain merge precedence as: main config, then extends, then remotes, then lefthook-local.*.
• When using the phrase "best practice", ground exact behavior in the bundled docs and schema, and treat blog-derived patterns as workflow guidance rather than hard requirements.

When reviewing an existing config, call out:

• commands that will not match any files because placeholders and filters do not align;
• rewriters that forgot stage_fixed: true;
• file-wide commands incorrectly using {staged_files};
• unnecessary complexity where commands would be enough;
• local overrides that should live in lefthook-local.* instead of shared config.

Use Bundled Resources

• For a quick starting point, copy assets/minimal-pre-commit.yml. For JS or TS repos, copy assets/js-ts-pre-commit.yml. Then adapt the package manager and commands to the repo.
• Load references/patterns.md for concrete recipes before drafting a non-trivial config.
• Load references/best-practices.md when the user explicitly asks for recommendations or wants rationale backed by real-world Lefthook usage.
• Load references/schema-cheatsheet.md when exact option spelling or allowed nesting matters.
• Keep explanations compact in the final answer. Include only the options that matter for the current repository.