Core Web Vitals are user-experience metrics centered on loading, responsiveness, and visual stability. The current metrics are Largest Contentful Paint, Interaction to Next Paint, and Cumulative Layout Shift. They can be observed through real-user field data, while lab tools help diagnose performance in a controlled test.
What each metric describes
- Largest Contentful Paint measures when the main visible content finishes rendering.
- Interaction to Next Paint measures responsiveness across user interactions during a visit.
- Cumulative Layout Shift measures unexpected movement of visible content.
Field data and lab data answer different questions
Chrome UX Report data reflects eligible visits from real Chrome users over a rolling period. Lighthouse and PageSpeed lab results run a simulated load under defined conditions. Field data tells you what users experienced. Lab data gives a repeatable environment for finding likely causes and testing changes.
Monitor by page type and device
Templates often share performance characteristics. Group product pages, articles, location pages, and other page types, then review mobile and desktop separately. A template-level pattern usually gives engineering teams a clearer starting point than a site-wide average.
Turn scores into diagnosis
Use the metric trend to identify affected URLs, then inspect the underlying opportunities and page behavior. Common investigations include render-blocking resources, oversized media, long main-thread tasks, late-loaded fonts, and elements without reserved dimensions. Validate the deployed change in lab tests first, then watch field data as new visits enter the rolling window.