Overview
This page is the atomic definition. Measurement and optimization guidance lives at core-web-vitals and technical.
Definition
Web Vitals is Google’s framework for quantifying user experience on the web, introduced in 2020. It defines metrics across three user experience pillars: loading (how fast does content appear), interactivity (how fast does the page respond to input), and visual stability (does content shift unexpectedly during load). The Core Web Vitals subset consists of three metrics that are incorporated into Google’s ranking algorithm: Largest Contentful Paint (lcp, targeting under 2.5 seconds), Interaction to Next Paint (inp, targeting under 200 ms), and Cumulative Layout Shift (cls, targeting under 0.1). These metrics are collected from real Chrome users via the Chrome User Experience Report (CrUX) and from synthetic tests in tools like Lighthouse and PageSpeed Insights. Improvements to rendering strategy, such as switching from csr to ssg or ssr, often have direct positive effects on LCP. Eliminating render-blocking resources, lazy-loading images, and using size attributes on media reduces CLS.
When it applies
Measure Web Vitals on every public-facing page. Pay particular attention to the 75th percentile of field data, which is the threshold Google uses for ranking assessment. Laboratory metrics from Lighthouse are useful for debugging but do not substitute for CrUX field data.
Example
A landing page switches from CSR to SSG. LCP drops from 3.8 s to 1.2 s because the browser no longer waits for a JavaScript bundle before painting the hero image. The page moves from “Needs improvement” to “Good” in PageSpeed Insights within 28 days as CrUX data refreshes.
Related concepts
- lcp - Largest Contentful Paint; the loading Core Web Vital.
- inp - Interaction to Next Paint; the interactivity Core Web Vital.
- cls - Cumulative Layout Shift; the visual stability Core Web Vital.
- ssg - static generation is one of the most effective LCP improvements.
- technical - Core Web Vitals are a confirmed Google Search ranking factor.
Citing this term
See Web Vitals (llmbestpractices.com/glossary/web-vitals).