Why website speed matters: Core Web Vitals in plain language

Visitors leave slow websites, and search engines notice. Google's Core Web Vitals turn "does this page feel fast?" into three measurable numbers.

The three metrics

Largest Contentful Paint (LCP) — how long until the main content, usually the hero image or headline, appears. Aim for 2.5 seconds or less.

Interaction to Next Paint (INP) — how quickly the page responds when someone taps or clicks. It replaced First Input Delay in 2024. Aim for 200 milliseconds or less.

Cumulative Layout Shift (CLS) — how much the page jumps around while loading, like a button moving just as you tap it. Aim for 0.1 or less.

Fixes that make the biggest difference

For LCP:

• Serve images in modern formats at the right size, and give the hero image priority
• Render pages on the server or pre-render them so HTML arrives ready
• Use a CDN and caching so pages are close to your readers

For INP:

• Ship less JavaScript; move heavy work off the main thread
• Avoid giant components that re-render on every keystroke

For CLS:

• Always set width and height (or an aspect ratio) on images and embeds
• Reserve space for ads and banners
• Load web fonts with sensible fallbacks

How to measure

Use PageSpeed Insights for a quick report, the Chrome DevTools Performance panel for detail, and Search Console to see real-user data across your whole site. Lab tests are useful, but field data from real visitors is what counts.

The bottom line

Fast, stable pages keep readers around longer. The good news is that most of the gains come from a few habits: smaller images, less JavaScript and reserved space for everything that loads late.