# Lighthouse — Automated Web Performance Auditing by Google

> An open-source tool by Google that audits web pages for performance, accessibility, SEO, and best practices, available in Chrome DevTools, as a CLI, and as a Node module.

## Install

Save as a script file and run:

# Lighthouse — Automated Web Performance Auditing by Google

## Quick Use
```bash
# Install CLI globally
npm install -g lighthouse

# Run an audit
lighthouse https://example.com --output html --output-path report.html

# Or use Chrome DevTools > Lighthouse tab directly
```

## Introduction
Lighthouse is an automated auditing tool maintained by Google that evaluates web pages across five categories: Performance, Accessibility, Best Practices, SEO, and Progressive Web App compliance. It generates actionable reports that help developers identify and fix issues affecting user experience and search ranking.

## What Lighthouse Does
- Audits page load performance with metrics like LCP, FID, CLS, and TTFB
- Checks accessibility against WCAG guidelines and ARIA best practices
- Validates SEO fundamentals including meta tags, structured data, and crawlability
- Tests Progressive Web App criteria like service worker registration and manifest
- Produces HTML, JSON, or CSV reports with detailed recommendations

## Architecture Overview
Lighthouse drives a headless Chrome instance via the Chrome DevTools Protocol. It collects trace data, network logs, and DOM snapshots during a simulated page load, then runs a series of audits against the gathered artifacts. Each audit produces a score and diagnostic details. Results are aggregated into category scores weighted by impact.

## Self-Hosting & Configuration
- Run via Chrome DevTools Lighthouse tab with zero setup
- Install the CLI with npm for scripting and CI integration
- Use `--preset=desktop` or `--preset=perf` to customize throttling and emulation
- Configure custom audits or skip specific ones via a `--config-path` JSON file
- Integrate with CI using Lighthouse CI to track scores over time and set budgets

## Key Features
- Five audit categories covering performance, accessibility, best practices, SEO, and PWA
- Core Web Vitals metrics aligned with Google search ranking signals
- Lighthouse CI for automated regression testing in pull requests
- User flow mode for auditing multi-step interactions like checkout flows
- Timespan mode for measuring performance during specific user actions

## Comparison with Similar Tools
- **WebPageTest** — remote lab testing with waterfall charts; Lighthouse focuses on local audits with broader category coverage
- **PageSpeed Insights** — uses Lighthouse under the hood plus field data from CrUX; Lighthouse CLI runs locally
- **axe-core** — specialized accessibility testing; Lighthouse includes axe-based checks alongside performance and SEO
- **Unlighthouse** — scans entire sites using Lighthouse; Lighthouse audits one URL at a time by default
- **Chrome DevTools Performance tab** — raw trace analysis; Lighthouse provides scored, actionable recommendations

## FAQ
**Q: Are Lighthouse scores the same as PageSpeed Insights?**
A: PageSpeed Insights uses Lighthouse for lab data but also includes field data from the Chrome User Experience Report, so scores may differ.

**Q: Can I run Lighthouse in CI pipelines?**
A: Yes. Lighthouse CI (LHCI) is designed for this, with GitHub Actions support, budget assertions, and historical tracking.

**Q: How do I audit authenticated pages?**
A: Use the `--extra-headers` flag to pass auth tokens, or use Lighthouse's user flow API to script login before auditing.

**Q: Does Lighthouse support mobile and desktop emulation?**
A: Yes. By default it simulates a mid-tier mobile device. Use `--preset=desktop` for desktop emulation with no throttling.

## Sources
- https://github.com/GoogleChrome/lighthouse
- https://developer.chrome.com/docs/lighthouse/

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Source: https://tokrepo.com/en/workflows/ac7ff133-4384-11f1-9bc6-00163e2b0d79
Author: Script Depot