Pre Commit

Pre-commit Hooks

Automate code quality checks with pre-commit hooks.

Quick Reference

1. Pre-commit (Python Framework)

Installation

# Install pre-commit
pip install pre-commit

# Install hooks in repository
pre-commit install

# Install commit-msg hook (for conventional commits)
pre-commit install --hook-type commit-msg

Configuration (.pre-commit-config.yaml)

repos:
  # General hooks
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v4.5.0
    hooks:
      - id: trailing-whitespace
      - id: end-of-file-fixer
      - id: check-yaml
      - id: check-json
      - id: check-added-large-files
        args: ['--maxkb=500']
      - id: check-merge-conflict
      - id: detect-private-key
      - id: check-case-conflict

  # Python
  - repo: https://github.com/psf/black
    rev: 24.1.1
    hooks:
      - id: black

  - repo: https://github.com/astral-sh/ruff-pre-commit
    rev: v0.1.14
    hooks:
      - id: ruff
        args: [--fix]
      - id: ruff-format

  - repo: https://github.com/pre-commit/mirrors-mypy
    rev: v1.8.0
    hooks:
      - id: mypy
        additional_dependencies: [types-requests]

  # JavaScript/TypeScript
  - repo: https://github.com/pre-commit/mirrors-eslint
    rev: v8.56.0
    hooks:
      - id: eslint
        files: \.[jt]sx?$
        types: [file]
        additional_dependencies:
          - eslint@8.56.0
          - typescript
          - '@typescript-eslint/parser'
          - '@typescript-eslint/eslint-plugin'

  - repo: https://github.com/pre-commit/mirrors-prettier
    rev: v4.0.0-alpha.8
    hooks:
      - id: prettier
        types_or: [javascript, jsx, ts, tsx, json, yaml, markdown]

  # Security
  - repo: https://github.com/Yelp/detect-secrets
    rev: v1.4.0
    hooks:
      - id: detect-secrets
        args: ['--baseline', '.secrets.baseline']

  - repo: https://github.com/gitleaks/gitleaks
    rev: v8.18.1
    hooks:
      - id: gitleaks

  # Conventional commits
  - repo: https://github.com/compilerla/conventional-pre-commit
    rev: v3.1.0
    hooks:
      - id: conventional-pre-commit
        stages: [commit-msg]

default_language_version:
  python: python3.11
  node: 20.10.0

ci:
  autofix_prs: true
  autoupdate_schedule: weekly

Commands

# Run on all files
pre-commit run --all-files

# Run specific hook
pre-commit run black --all-files

# Update hooks to latest versions
pre-commit autoupdate

# Skip hooks temporarily
git commit --no-verify -m "message"
# or
SKIP=black,ruff git commit -m "message"

# Clean cache
pre-commit clean
pre-commit gc

2. Husky + lint-staged (Node.js)

Installation

# Install husky
npm install -D husky lint-staged
npx husky init

# This creates .husky directory with pre-commit hook

Configuration

// package.json
{
  "scripts": {
    "prepare": "husky"
  },
  "lint-staged": {
    "*.{js,jsx,ts,tsx}": [
      "eslint --fix",
      "prettier --write"
    ],
    "*.{json,md,yml,yaml}": [
      "prettier --write"
    ],
    "*.css": [
      "stylelint --fix",
      "prettier --write"
    ]
  }
}

# .husky/pre-commit
npx lint-staged

Commit Message Hook

# .husky/commit-msg
npx --no -- commitlint --edit $1

// commitlint.config.js
module.exports = {
  extends: ['@commitlint/config-conventional'],
  rules: {
    'type-enum': [
      2,
      'always',
      ['feat', 'fix', 'docs', 'style', 'refactor', 'test', 'chore', 'ci']
    ],
    'subject-case': [2, 'always', 'lower-case'],
    'header-max-length': [2, 'always', 72]
  }
};

3. Common Hook Configurations

Python Project

# .pre-commit-config.yaml
repos:
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v4.5.0
    hooks:
      - id: trailing-whitespace
      - id: end-of-file-fixer
      - id: check-yaml
      - id: check-toml
      - id: check-added-large-files

  - repo: https://github.com/astral-sh/ruff-pre-commit
    rev: v0.1.14
    hooks:
      - id: ruff
        args: [--fix, --exit-non-zero-on-fix]
      - id: ruff-format

  - repo: https://github.com/pre-commit/mirrors-mypy
    rev: v1.8.0
    hooks:
      - id: mypy
        additional_dependencies:
          - types-requests
          - pydantic

  - repo: https://github.com/python-poetry/poetry
    rev: 1.7.0
    hooks:
      - id: poetry-check
      - id: poetry-lock
        args: [--check]

  - repo: local
    hooks:
      - id: pytest
        name: pytest
        entry: pytest
        language: system
        pass_filenames: false
        always_run: true
        stages: [push]

JavaScript/TypeScript Project

repos:
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v4.5.0
    hooks:
      - id: trailing-whitespace
      - id: end-of-file-fixer
      - id: check-json
      - id: check-yaml

  - repo: local
    hooks:
      - id: eslint
        name: eslint
        entry: npx eslint --fix
        language: system
        files: \.[jt]sx?$
        pass_filenames: true

      - id: prettier
        name: prettier
        entry: npx prettier --write
        language: system
        files: \.(js|jsx|ts|tsx|json|md|yml|yaml)$

      - id: tsc
        name: typescript
        entry: npx tsc --noEmit
        language: system
        files: \.tsx?$
        pass_filenames: false

      - id: test
        name: tests
        entry: npm test
        language: system
        pass_filenames: false
        stages: [push]

Go Project

repos:
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v4.5.0
    hooks:
      - id: trailing-whitespace
      - id: end-of-file-fixer
      - id: check-yaml

  - repo: https://github.com/dnephin/pre-commit-golang
    rev: v0.5.1
    hooks:
      - id: go-fmt
      - id: go-vet
      - id: go-imports
      - id: go-cyclo
        args: [-over=15]
      - id: golangci-lint
      - id: go-build
      - id: go-mod-tidy

Terraform/IaC Project

repos:
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v4.5.0
    hooks:
      - id: trailing-whitespace
      - id: end-of-file-fixer
      - id: check-yaml
      - id: check-json

  - repo: https://github.com/antonbabenko/pre-commit-terraform
    rev: v1.86.0
    hooks:
      - id: terraform_fmt
      - id: terraform_validate
      - id: terraform_tflint
      - id: terraform_docs
        args:
          - --hook-config=--path-to-file=README.md
          - --hook-config=--add-to-existing-file=true
          - --hook-config=--create-file-if-not-exist=true
      - id: terraform_checkov
        args:
          - --args=--skip-check CKV_AWS_1

  - repo: https://github.com/bridgecrewio/checkov.git
    rev: 3.1.50
    hooks:
      - id: checkov

4. Security Hooks

repos:
  # Detect secrets
  - repo: https://github.com/Yelp/detect-secrets
    rev: v1.4.0
    hooks:
      - id: detect-secrets
        args: ['--baseline', '.secrets.baseline']
        exclude: package-lock\.json$

  # Gitleaks
  - repo: https://github.com/gitleaks/gitleaks
    rev: v8.18.1
    hooks:
      - id: gitleaks

  # Trivy
  - repo: https://github.com/aquasecurity/trivy
    rev: v0.48.3
    hooks:
      - id: trivy-config
      - id: trivy-fs
        args: ['--scanners', 'vuln,secret']

  # Bandit (Python security)
  - repo: https://github.com/PyCQA/bandit
    rev: 1.7.7
    hooks:
      - id: bandit
        args: ['-c', 'pyproject.toml']
        additional_dependencies: ['bandit[toml]']

5. CI Integration

GitHub Actions

name: Pre-commit

on:
  pull_request:
  push:
    branches: [main]

jobs:
  pre-commit:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: actions/setup-python@v5
        with:
          python-version: '3.11'

      - uses: pre-commit/action@v3.0.1
        with:
          extra_args: --all-files

pre-commit.ci

# .pre-commit-config.yaml
ci:
  autofix_prs: true
  autofix_commit_msg: 'style: auto fixes from pre-commit.ci'
  autoupdate_schedule: weekly
  autoupdate_commit_msg: 'chore: pre-commit autoupdate'
  skip: [pytest]  # Skip slow hooks in CI

6. Lefthook (Alternative)

Installation

# Install
npm install -D lefthook
# or
brew install lefthook

# Initialize
lefthook install

Configuration (lefthook.yml)

pre-commit:
  parallel: true
  commands:
    lint:
      glob: "*.{js,ts,jsx,tsx}"
      run: npx eslint --fix {staged_files}

    format:
      glob: "*.{js,ts,jsx,tsx,json,md}"
      run: npx prettier --write {staged_files}

    test:
      run: npm test -- --passWithNoTests
      skip:
        - merge
        - rebase

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

pre-push:
  commands:
    typecheck:
      run: npx tsc --noEmit

Best Practices

1. Fast hooks - Keep pre-commit hooks under 5 seconds
2. Staged files only - Use lint-staged for efficiency
3. Skip for emergencies - --no-verify when needed
4. CI verification - Run hooks in CI as backup
5. Auto-fix when possible - --fix flags
6. Push hooks for slow checks - Tests, type checking
7. Baseline secrets - Track known false positives
8. Pin versions - Reproducible environments
9. Documentation - README for setup instructions
10. Team alignment - Everyone uses same hooks

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