Google Lighthouse

Lighthouse is a free, open-source, automated tool developed by Google to enhance the quality of web pages. It performs audits across several categories and generates detailed reports highlighting a website's strengths and areas for improvement. This makes Lighthouse an essential resource for developers seeking to optimize their websites for better functionality and compliance with modern web standards.

Google Lighthouse Audit Categories

Google Lighthouse performs the following audits:

• Performance: the Lighthouse Performance audit evaluates a webpage's speed, responsiveness, and interactivity using a set of Web Vitals metrics, with a primary focus on Core Web Vitals. There are six metrics tracked in this section:

1. Largest Contentful Paint (LCP): measures the time for the largest visible content element to render - refers to loading performance.
2. First Contentful Paint (FCP): captures the time until the first visible content appears - refers to perceived load speed.
3. Speed Index (SI): evaluates how quickly the visual content is populated during loading - refers to visual completion speed.
4. Time to Interactive (TTI): measures the time until the page is fully interactive; indicates readiness for user interaction (deprecated in Lighthouse 10).
5. Cumulative Layout Shift (CLS): tracks unexpected layout shifts - refers to visual stability.
6. Total Blocking Time (TBT): measures time when the page is unresponsive to user input during loading - refers to responsiveness.

• Accessibility: the Lighthouse Accessibility report relies on Web Content Accessibility Guidelines (WCAG) and related best practices to evaluate how well a website supports users with disabilities. It uses automated checks (like screen reader compatibility and color contrast) to assess various elements of a webpage that contribute to an inclusive and accessible user experience.

• SEO: the Lighthouse search engine optimization (SEO) report evaluates a webpage's adherence to essential SEO best practices, focusing on metadata, mobile-friendliness, indexability, structured data, crawlable links, and proper content formatting (e.g., headings and alt text). It also checks HTTPS security and highlights performance issues that may indirectly impact SEO. This ensures the site meets technical requirements for search engine visibility and optimization.

• Best Practices: the Lighthouse Best Practices report assesses a website’s adherence to modern standards, focusing on security (e.g., HTTPS, avoiding vulnerabilities), browser compatibility, efficient resource use (e.g., compressed images, minimal unused code), error-free interactions (e.g., no mixed content or broken links), and optimized media usage. It ensures websites are secure, efficient, and aligned with current development practices.

• Progressive Web App (PWA): the Lighthouse Progressive Web App (PWA) report evaluates a website's ability to function like a native app, focusing on service workers for offline functionality, a valid web app manifest for installability, secure HTTPS delivery, and responsive design. It checks performance, user engagement features (e.g., splash screens and app-like interactions), and offline reliability, ensuring the site meets PWA standards for a fast, secure, and engaging experience.

Google Lighthouse Audit Scores

The Performance, Accessibility, SEO, and Best Practices audits are scored on a scale of 0–100.

For the Progressive Web App (PWA) audit, the score is established on precise criteria evaluated as pass/fail, evaluating the implementation of PWA standards.

Google Lighthouse Accessibility

The tool can be run via:

• Chrome DevTools.
• Lighthouse Chrome extension.
• a website.
• a Node module.

Lighthouse will conduct multiple audits by submitting a URL and providing actionable suggestions to improve the website.