What are Core Web Vitals?

Core Web Vitals, explained

Each metric measures one thing people notice. Largest Contentful Paint (LCP) is how long it takes for the main content, usually the hero image or headline, to appear. Interaction to Next Paint (INP) is how quickly the page responds when someone taps or clicks. Cumulative Layout Shift (CLS) is how much things jump around while the page loads.

Google's targets for a good experience: LCP within 2.5 seconds of the page starting to load, INP under 200 milliseconds, and CLS under 0.1. INP replaced the older First Input Delay metric as a Core Web Vital on March 12, 2024, because it measures all interactions, not just the first one.

The numbers that count come from real users in the Chrome UX Report, which is what Search Console's Core Web Vitals report shows. Lab tools like Lighthouse are useful for debugging, but a perfect Lighthouse score on your laptop doesn't mean your field data passes on mid-range phones.

How much do they affect rankings? Google says good Core Web Vitals align with what its core ranking systems seek to reward, as part of a broader page experience. In practice they act more like a tiebreaker than a lever: great content on a slow page usually beats thin content on a fast one. But a slow, jumpy page loses users whatever Google thinks.

Common fixes on modern stacks: serve images in modern formats with explicit width and height (fixes CLS and LCP), preload the hero image, avoid layout-shifting cookie banners and ads, ship less client-side JavaScript, and render pages on the server or at build time. Static Next.js pages on a CDN tend to pass without special effort.

Why it matters for founders

Speed matters most on mobile, where many of your first visitors come from. You don't need perfect scores, but failing pages lose visitors and give up a signal Google does use.

Example

A landing page's LCP is 4 seconds because a 2MB PNG hero loads late. Converting it to WebP, adding width and height, and preloading it brings LCP under 2.5 seconds in field data a few weeks later.

Common mistakes

• Optimizing Lighthouse lab scores and ignoring field data.
• Images without width and height, which cause layout shift.
• Heavy client-side JavaScript on pages that could be static.
• Expecting speed fixes to outrank better content.