SYS/DEF
Core Web Vitals
LCP, INP, CLS: three field measures of real experience, at the 75th percentile — not a lab Lighthouse score.
Definition
Core Web Vitals are three field metrics (CrUX): Largest Contentful Paint (LCP, loading), Interaction to Next Paint (INP, responsiveness), Cumulative Layout Shift (CLS, visual stability). Google evaluates them at the 75th percentile of visits, mobile and desktop separate. A 100 Lighthouse in the lab with a warm cache is not a Vital.
They are one ranking signal among others, and a CRO signal: a page that jumps on click, or takes 4 s to paint the hero, converts less — even if the keyword is well targeted.
When it matters
Before a SEA campaign (Quality Score and bounce), before calling a landing “ready”, and when Search Console flags a URL group red. They also matter in A/B: a heavier variant (autoplay video, late font) can win the copy test and lose the Vital — the lab lift does not survive the field.
Shamalo’s landing diagnostic recalls them as a checklist, not a fetish: proof and CTA remain the core.
Pitfalls
Optimising the lab score by dumping LCP onto a placeholder. Ignoring INP after FID died. Measuring CLS without webfonts. Believing a green Vital “makes a page rank” with no intent and no E-E-A-T. Forcing an A/B that injects a banner and breaks CLS for the whole cohort.
Related terms
Related tool
Scored checklist: information, CTA, proof, speed, SEO basics — including what Vitals will not fix: Open landing page diagnostic.