Lighthouse Performance ScoreWhat it checks and how to fix it

What it checks

Reads the Performance category score from a Lighthouse run on the page, simulating a mid-range phone on a slow 4G connection. A score of 90 or above passes, 50 to 89 warns, and below 50 fails. It runs on the pages chosen for Lighthouse.

Why it matters

The Performance score is a weighted blend of First Contentful Paint, Largest Contentful Paint, Total Blocking Time, Cumulative Layout Shift and Speed Index, the same lab test PageSpeed Insights runs. It is deliberately pessimistic, but a low score reliably means the page is slow on ordinary phones, and slow pages lose visitors and conversions.

How to fix it

Run Lighthouse in Chrome DevTools (or PageSpeed Insights) on mobile and start with the opportunities that promise the largest savings. The fixes that move the score most:

• Compress images, serve them as WebP or AVIF, and lazy-load those below the fold.
• Load scripts with defer or async and remove JavaScript the page does not use.
• Inline critical CSS and load the rest without blocking rendering.
• Enable Brotli or gzip, long-lived caching headers and a CDN.
• Give images and embeds explicit dimensions so the layout does not shift.

<link rel="preload" href="/images/hero.webp" as="image" fetchpriority="high">
<script src="/assets/app.js" defer></script>

Aim for 90 or more and re-run Lighthouse after each change.