Standard Definition
Core Web Vitals are Google's standardized performance metrics for quantitatively evaluating the user experience of a webpage. Three main metrics: LCP (Largest Contentful Paint) measures the loading speed of the largest visible content element — target under 2.5 seconds. INP (Interaction to Next Paint) measures responsiveness to user interactions — target under 200 milliseconds, replaced FID (First Input Delay) as official metric in March 2024. CLS (Cumulative Layout Shift) measures visual stability, that is, how much layout shift occurs during loading — target below 0.1. Since the Page Experience Update 2021, Core Web Vitals feed into Google ranking, measured via real user data from the Chrome User Experience Report.
What this means in mandate practice
Core Web Vitals are often misweighted in practice — either underestimated or overestimated.
First, Core Web Vitals are a tie-breaker factor, not the primary ranking lever. When two pages are comparable in content and authority, the difference in Core Web Vitals can be decisive. But: an excellent LCP value will not make weak content top-ranking. The right prioritization logic: first content substance, then technical optimization — not the other way around.
Second, LCP value is often dominated by unoptimized images. In mandate analyses, the main image of the hero section is often the LCP element. Optimization levers are then: WebP or AVIF formats, correct image sizes per viewport, lazy loading for non-visible images, server-side image compression. An LCP improvement from 4.5 to 1.8 seconds is often achievable with these measures in 4-8 hours — the most economical CWV lever overall.
Third, INP is the most demanding of the three metrics. While LCP and CLS are primarily improved through asset optimization, INP depends on JavaScript execution quality — heavy event handlers, blocking calculations, inefficient framework configurations. INP problems are often only solvable through code reviews and refactoring, not through configuration adjustments. Those running an SPA architecture without server-side rendering struggle structurally with INP — which is one of the migration arguments to SSR frameworks.