Core Web Vitals

Core Web Vitals are Google’s three page-experience metrics that measure how a page feels to real users: how fast the main content loads, how quickly the page responds to input, and how stable the layout is while loading. They come from field data (the Chrome User Experience Report), not lab tests, and they feed Google’s page-experience signals.

The three metrics

• LCP (Largest Contentful Paint) — how long the largest visible element takes to render; the loading measure.
• INP (Interaction to Next Paint) — how quickly the page responds to user interactions; this replaced First Input Delay (FID) in March 2024.
• CLS (Cumulative Layout Shift) — how much the layout moves around during load; the stability measure.

A URL passes only when all three sit in the “good” range at the 75th percentile of visits.

Where it applies

Any page that ranks, though the payoff varies:

• Ecommerce — slow product and category pages lose both rankings and conversions.
• Publishing — ad and embed scripts are the usual cause of poor INP and CLS.
• Mobile-heavy sites — vitals are judged on the mobile rendering, where constraints are tightest.

What matters from each seat

• In-house — treat vitals as a shared performance budget, not a one-time fix; they drift as features ship.
• Engineering — most gains come from image handling, render-blocking scripts, and reserving space for late-loading elements.
• Brand — page experience is a tiebreaker, not a substitute for relevance; fix it, but don’t expect it to outrank better content.