Core Web Vitals (CWV)
A set of three specific metrics defined by Google that measure real-world user experience for page loading speed, interactivity, and visual stability: Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS).
Core Web Vitals are part of Google's page experience signals and directly influence search rankings. The thresholds for 'good' scores are: LCP under 2.5 seconds, INP under 200 milliseconds, and CLS under 0.1. These metrics are measured using real user data (field data from the Chrome User Experience Report) and can also be tested in lab conditions using Lighthouse, PageSpeed Insights, or Chrome DevTools.
Core Web Vitals shift performance from a developer concern to a cross-team priority. Poor scores affect SEO rankings, user satisfaction, and conversion rates.
Why It Matters for QA Teams
Core Web Vitals directly impact search rankings and user experience. QA teams that monitor these metrics can catch performance regressions before they hurt traffic and conversions.
Example
After deploying a new image carousel on the homepage, the QA team notices that the LCP score degraded from 1.8s to 3.4s (failing the 2.5s threshold) because the carousel loads a full-resolution hero image before optimizing it. They flag the regression, and the team implements responsive image loading with srcset and lazy loading.