Definition
Core Web Vitals are three Google-defined user-experience signals: Largest Contentful Paint (LCP, the speed of visible content loading), Interaction to Next Paint (INP, the responsiveness of the page to user input), and Cumulative Layout Shift (CLS, the visual stability of the page during load). Targets are LCP under 2.5 seconds, INP under 200 milliseconds, CLS under 0.1.
Why Core Web Vitals matter
Google uses Core Web Vitals as a ranking signal for mobile search. Sites that fail the thresholds rank lower than equivalent sites that pass. Beyond ranking, Core Web Vitals correlate strongly with conversion: each 100ms of LCP improvement is worth roughly 1 percent conversion lift up to about 2.5 seconds.
The three metrics in detail
LCP (Largest Contentful Paint): time from page request to the moment the largest above-fold element (usually the hero image or main text block) becomes visible. Target: under 2.5 seconds.
INP (Interaction to Next Paint): how long interactions block the main thread. Replaced FID in March 2024. Target: under 200 milliseconds. The thresholds are tight; many Magento stores fail INP without realizing.
CLS (Cumulative Layout Shift): how much content jumps during page load. Target: under 0.1. Often caused by analytics banners, ads, or images without declared dimensions loading after first paint.