Lighthouseレポートの読み解き方

Welcome to interpreting Lighthouse reports! After running an audit, you'll get a detailed report. But what do all those numbers and recommendations mean?

Understanding your report is key to making your website faster and more user-friendly. It's like a diagnostic tool for your site's health.

A Lighthouse report organizes its findings into several main categories, each with its own score and recommendations. These categories help you focus on different aspects of your site.

• Performance: How fast your site loads and becomes interactive.
• Accessibility: How usable your site is for people with disabilities.
• Best Practices: Adherence to modern web development standards.
• SEO: How well your site is optimized for search engine ranking.
• Progressive Web App (PWA): Checks for PWA features (if applicable).

The Performance section gives you an overall score (0-100) and details on individual metrics. A higher score means a faster, more responsive site.

Key metrics you'll see here include:

• First Contentful Paint (FCP): When the first content appears.
• Largest Contentful Paint (LCP): When the main content loads.
• Total Blocking Time (TBT): How long the main thread is blocked.
• Cumulative Layout Shift (CLS): How much content unexpectedly moves.
• Speed Index: How quickly content is visually displayed.

Below the scores, you'll find 'Opportunities'. This section highlights potential improvements that can significantly speed up your page load. Each opportunity often comes with an estimated time saving.

• Example: 'Eliminate render-blocking resources' suggests JavaScript or CSS files are delaying your page display.
• Example: 'Serve images in next-gen formats' recommends using more efficient image types like WebP.

These are often the easiest wins!

The 'Diagnostics' section offers more technical details about how your page performs. These are advanced insights for developers to pinpoint specific issues impacting performance.

• Example: 'Avoid chaining critical requests' helps you understand the order resources are loaded.
• Example: 'Minimize main-thread work' points to heavy JavaScript execution.

While 'Opportunities' focus on quick fixes, 'Diagnostics' help you understand the root causes.

Don't just focus on the negatives! The 'Passed Audits' section lists all the checks your website successfully passed. This is a great way to see what you're already doing right.

It provides positive reinforcement and confirms that certain aspects of your site are already optimized according to Lighthouse's standards. Keep up the good work!

The Accessibility section ensures your website is usable by as many people as possible, including those with disabilities. A high score here means your site is inclusive.

Common issues flagged include:

• Missing alt text for images.
• Insufficient color contrast for text.
• Elements with non-unique IDs.
• Incorrect ARIA attributes.

Fixing these improves the experience for all users.

This section checks for adherence to general web development best practices. It helps ensure your site is secure, robust, and performs well across different browsers and devices.

Examples of checks include:

• Using HTTPS.
• Avoiding deprecated APIs.
• Properly handling browser errors.
• Ensuring images have correct aspect ratios.

A good score here indicates a well-built, modern website.

The SEO (Search Engine Optimization) section evaluates how well your website is optimized for search engine crawlers. A good SEO score helps your site appear higher in search results.

Lighthouse checks for things like:

• Valid meta tags (title, description).
• Having a valid robots.txt file.
• Properly structured content.
• Links are crawlable.

These checks help search engines understand and rank your content.

Great job! You now have a solid understanding of how to interpret a Lighthouse report. Remember, it's not just about the final score; it's about understanding the specific recommendations.

Use the 'Opportunities' for quick wins and 'Diagnostics' for deeper technical issues. By regularly reviewing these reports, you can continuously improve your website's performance and provide a better experience for all users. Keep auditing and optimizing!