Master Web
Performance

Core Web Vitals are three field metrics Google uses to measure real-world user experience: Largest Contentful Paint (LCP) for loading speed, Cumulative Layout Shift (CLS) for visual stability, and Interaction to Next Paint (INP) for responsiveness. Google reports a fourth supporting metric, Time to First Byte (TTFB), but only LCP, CLS, and INP currently feed the Page Experience signal in Search.

LCP under 2.5 seconds is Good, 2.5 to 4.0 seconds is Needs Improvement, and above 4.0 seconds is Poor. CLS under 0.1 is Good, 0.1 to 0.25 is Needs Improvement, above 0.25 is Poor. INP under 200 milliseconds is Good, 200 to 500 milliseconds is Needs Improvement, above 500 milliseconds is Poor. A page passes Core Web Vitals overall when the 75th percentile of real users hits Good on all three metrics over a rolling 28-day window.

Yes, but as a tiebreaker, not as a primary ranking factor. Google treats Page Experience signals (including Core Web Vitals) as a secondary input that can decide ranking between pages of similar relevance. A fast page does not outrank a more relevant slow page, but among comparable results, Core Web Vitals scores can shift position by one or two slots. The larger SEO benefit usually comes from secondary effects: lower bounce rates, more engaged sessions, and better crawl budget utilization.

Field data (the data Google uses for ranking) comes from the Chrome User Experience Report, which aggregates anonymized measurements from real Chrome users who have opted in. You can query this dataset directly through the CrUX API, or view your own site's aggregated data in Google Search Console under the Core Web Vitals report. Lab tools like Lighthouse and PageSpeed Insights run synthetic tests in a controlled environment; their scores often differ from field data and should be used to guide development, not to validate production performance.