Git Hooks Automation

Git Hooks Automation

Automate code quality enforcement at the Git level. Set up hooks that lint, format, test, and validate before commits and pushes ever reach your CI pipeline — catching issues in seconds instead of minutes.

When to Use This Skill

• User asks to "set up git hooks" or "add pre-commit hooks"
• Configuring Husky, lint-staged, or the pre-commit framework
• Enforcing commit message conventions (Conventional Commits, commitlint)
• Automating linting, formatting, or type-checking before commits
• Setting up pre-push hooks for test runners
• Migrating from Husky v4 to v9+ or adopting hooks from scratch
• User mentions "pre-commit", "commit-msg", "pre-push", "lint-staged", or "githooks"

Git Hooks Fundamentals

Git hooks are scripts that run automatically at specific points in the Git workflow. They live in .git/hooks/ and are not version-controlled by default — which is why tools like Husky exist.

Hook Types & When They Fire

Native Git Hooks (No Framework)

# Create a pre-commit hook manually
cat > .git/hooks/pre-commit << 'EOF'
#!/bin/sh
set -e

# Run linter on staged files only
STAGED_FILES=$(git diff --cached --name-only --diff-filter=ACM | grep -E '\.(js|ts|jsx|tsx)$' || true)

if [ -n "$STAGED_FILES" ]; then
  echo "🔍 Linting staged files..."
  echo "$STAGED_FILES" | xargs npx eslint --fix
  echo "$STAGED_FILES" | xargs git add  # Re-stage after fixes
fi
EOF
chmod +x .git/hooks/pre-commit

Problem: .git/hooks/ is local-only and not shared with the team. Use a framework instead.

Husky + lint-staged (Node.js Projects)

The modern standard for JavaScript/TypeScript projects. Husky manages Git hooks; lint-staged runs commands only on staged files for speed.

Quick Setup (Husky v9+)

# Install
npm install --save-dev husky lint-staged

# Initialize Husky (creates .husky/ directory)
npx husky init

# The init command creates a pre-commit hook — edit it:
echo "npx lint-staged" > .husky/pre-commit

Configure lint-staged in package.json

{
  "lint-staged": {
    "*.{js,jsx,ts,tsx}": [
      "eslint --fix --max-warnings=0",
      "prettier --write"
    ],
    "*.{css,scss}": [
      "prettier --write",
      "stylelint --fix"
    ],
    "*.{json,md,yml,yaml}": [
      "prettier --write"
    ]
  }
}

Add Commit Message Linting

# Install commitlint
npm install --save-dev @commitlint/cli @commitlint/config-conventional

# Create commitlint config
cat > commitlint.config.js << 'EOF'
module.exports = {
  extends: ['@commitlint/config-conventional'],
  rules: {
    'type-enum': [2, 'always', [
      'feat', 'fix', 'docs', 'style', 'refactor',
      'perf', 'test', 'build', 'ci', 'chore', 'revert'
    ]],
    'subject-max-length': [2, 'always', 72],
    'body-max-line-length': [2, 'always', 100]
  }
};
EOF

# Add commit-msg hook
echo "npx --no -- commitlint --edit \$1" > .husky/commit-msg

Add Pre-Push Hook

# Run tests before pushing
echo "npm test" > .husky/pre-push

Complete Husky Directory Structure

project/
├── .husky/
│   ├── pre-commit        # npx lint-staged
│   ├── commit-msg        # npx --no -- commitlint --edit $1
│   └── pre-push          # npm test
├── commitlint.config.js
├── package.json          # lint-staged config here
└── ...

pre-commit Framework (Python / Polyglot)

Language-agnostic framework that works with any project. Hooks are defined in YAML and run in isolated environments.

Setup

# Install (Python required)
pip install pre-commit

# Create config
cat > .pre-commit-config.yaml << 'EOF'
repos:
  # Built-in checks
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v4.6.0
    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

  # Python formatting
  - repo: https://github.com/psf/black
    rev: 24.4.2
    hooks:
      - id: black

  # Python linting
  - repo: https://github.com/astral-sh/ruff-pre-commit
    rev: v0.4.4
    hooks:
      - id: ruff
        args: ['--fix']
      - id: ruff-format

  # Shell script linting
  - repo: https://github.com/shellcheck-py/shellcheck-py
    rev: v0.10.0.1
    hooks:
      - id: shellcheck

  # Commit message format
  - repo: https://github.com/compilerla/conventional-pre-commit
    rev: v3.2.0
    hooks:
      - id: conventional-pre-commit
        stages: [commit-msg]
EOF

# Install hooks into .git/hooks/
pre-commit install
pre-commit install --hook-type commit-msg

# Run against all files (first time)
pre-commit run --all-files

Key Commands

pre-commit install              # Install hooks
pre-commit run --all-files      # Run on everything (CI or first setup)
pre-commit autoupdate           # Update hook versions
pre-commit run <hook-id>        # Run a specific hook
pre-commit clean                # Clear cached environments

Custom Hook Scripts (Any Language)

For projects not using Node or Python, write hooks directly in shell.

Portable Pre-Commit Hook

#!/bin/sh
# .githooks/pre-commit — Team-shared hooks directory
set -e

echo "=== Pre-Commit Checks ==="

# 1. Prevent commits to main/master
BRANCH=$(git symbolic-ref --short HEAD 2>/dev/null || echo "detached")
if [ "$BRANCH" = "main" ] || [ "$BRANCH" = "master" ]; then
  echo "❌ Direct commits to $BRANCH are not allowed. Use a feature branch."
  exit 1
fi

# 2. Check for debugging artifacts
if git diff --cached --diff-filter=ACM | grep -nE '(console\.log|debugger|binding\.pry|import pdb)' > /dev/null 2>&1; then
  echo "⚠️  Debug statements found in staged files:"
  git diff --cached --diff-filter=ACM | grep -nE '(console\.log|debugger|binding\.pry|import pdb)'
  echo "Remove them or use git commit --no-verify to bypass."
  exit 1
fi

# 3. Check for large files (>1MB)
LARGE_FILES=$(git diff --cached --name-only --diff-filter=ACM | while read f; do
  size=$(wc -c < "$f" 2>/dev/null || echo 0)
  if [ "$size" -gt 1048576 ]; then echo "$f ($((size/1024))KB)"; fi
done)
if [ -n "$LARGE_FILES" ]; then
  echo "❌ Large files detected:"
  echo "$LARGE_FILES"
  exit 1
fi

# 4. Check for secrets patterns
if git diff --cached --diff-filter=ACM | grep -nEi '(AKIA[0-9A-Z]{16}|sk-[a-zA-Z0-9]{48}|ghp_[a-zA-Z0-9]{36}|password\s*=\s*["\x27][^"\x27]+["\x27])' > /dev/null 2>&1; then
  echo "🚨 Potential secrets detected in staged changes! Review before committing."
  exit 1
fi

echo "✅ All pre-commit checks passed"

Share Custom Hooks via core.hooksPath

# In your repo, set a shared hooks directory
git config core.hooksPath .githooks

# Add to project setup docs or Makefile
# Makefile
setup:
	git config core.hooksPath .githooks
	chmod +x .githooks/*

CI Integration

Hooks are a first line of defense, but CI is the source of truth.

Run pre-commit in CI (GitHub Actions)

# .github/workflows/lint.yml
name: Lint
on: [push, pull_request]
jobs:
  pre-commit:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python@v5
        with:
          python-version: '3.12'
      - uses: pre-commit/action@v3.0.1

Run lint-staged in CI (Validation Only)

# Validate that lint-staged would pass (catch bypassed hooks)
name: Lint Check
on: [pull_request]
jobs:
  lint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: 20
      - run: npm ci
      - run: npx eslint . --max-warnings=0
      - run: npx prettier --check .

Common Pitfalls & Fixes

Hooks Not Running

Performance Issues

// ❌ Slow: runs on ALL files every commit
{
  "scripts": {
    "precommit": "eslint src/ && prettier --write src/"
  }
}

// ✅ Fast: lint-staged runs ONLY on staged files
{
  "lint-staged": {
    "*.{js,ts}": ["eslint --fix", "prettier --write"]
  }
}

Bypassing Hooks (When Needed)

# Skip all hooks for a single commit
git commit --no-verify -m "wip: quick save"

# Skip pre-push only
git push --no-verify

# Skip specific pre-commit hooks
SKIP=eslint git commit -m "fix: update config"

Warning: Bypassing hooks should be rare. If your team frequently bypasses, the hooks are too slow or too strict — fix them.

Migration Guide

Husky v4 → v9 Migration

# 1. Remove old Husky
npm uninstall husky
rm -rf .husky

# 2. Remove old config from package.json
# Delete "husky": { "hooks": { ... } } section

# 3. Install fresh
npm install --save-dev husky
npx husky init

# 4. Recreate hooks
echo "npx lint-staged" > .husky/pre-commit
echo "npx --no -- commitlint --edit \$1" > .husky/commit-msg

# 5. Clean up — old Husky used package.json config,
#    new Husky uses .husky/ directory with plain scripts

Adopting Hooks on an Existing Project

# Step 1: Start with formatting only (low friction)
# lint-staged config:
{ "*.{js,ts}": ["prettier --write"] }

# Step 2: Add linting after team adjusts (1-2 weeks later)
{ "*.{js,ts}": ["eslint --fix", "prettier --write"] }

# Step 3: Add commit message linting
# Step 4: Add pre-push test runner

# Gradual adoption prevents team resistance

Key Principles

• Staged files only — Never lint the entire codebase on every commit
• Auto-fix when possible — --fix flags reduce developer friction
• Fast hooks — Pre-commit should complete in < 5 seconds
• Fail loud — Clear error messages with actionable fixes
• Team-shared — Use Husky or core.hooksPath so hooks are version-controlled
• CI as backup — Hooks are convenience; CI is the enforcer
• Gradual adoption — Start with formatting, add linting, then testing

Related Skills

• @codebase-audit-pre-push - Deep audit before GitHub push
• @verification-before-completion - Verification before claiming work is done
• @bash-pro - Advanced shell scripting for custom hooks
• @github-actions-templates - CI/CD workflow templates