What are Core Web Vitals?

• LCP (Largest Contentful Paint). How long the biggest visible element, often a hero image or headline, takes to appear.
• INP (Interaction to Next Paint). How quickly the page reacts when someone taps or clicks. It replaced the older FID metric when it became a stable Core Web Vital in 2024¹.
• CLS (Cumulative Layout Shift). How much the layout jumps while loading. The button that moves just as you tap it is a CLS problem.

Google's web.dev documentation treats them as field metrics: measured on real visitors, with lab tests no substitute¹. A lab test on a fast laptop is not the same thing.

The thresholds are measured at the 75th percentile of page loads, split between mobile and desktop¹. In plain terms: three in four visits should be within the line, not just your own visit on office Wi-Fi.

Google's own wording is careful. Core Web Vitals, with other page experience aspects, align with what its core ranking systems seek to reward². That is not a promise of a ranking jump. So do not buy them as an SEO trick. For how this fits with newer terms, read AEO vs GEO vs SEO, and for the basics see SEO.

Because of the shopper, not the algorithm. A slow product page and a jumping checkout button cost orders. That is a conversion rate question, and a landing page question if the page sits behind an ad.

Do not take it on faith that a speed fix raised sales. Measure it. An A/B test splits visitors between two versions at random, so you see what the change did to orders, not just to the score.

You can see your own results in the Core Web Vitals report in Search Console.

For ZFD: We treat a speed fix as a hypothesis about sales and test it like one.