What Are Core Web Vitals?
Core Web Vitals are a set of three specific metrics that Google uses to measure user experience on web pages. They are: Largest Contentful Paint (LCP) — measures loading performance, First Input Delay (FID) — measures interactivity, and Cumulative Layout Shift (CLS) — measures visual stability. These metrics are part of Google's Page Experience signals.
Why It Matters
Core Web Vitals are a confirmed Google ranking signal. Pages with good CWV scores may receive a ranking boost in Google Search. More importantly, they directly impact user experience — slow loading, delayed interactivity, and unexpected layout shifts cause users to abandon your site.
How AuditMe Detects It
AuditMe retrieves Core Web Vitals from two sources: (1) Chrome User Experience Report (CrUX) — real-user field data from Chrome browsers, providing 28-day rolling averages, and (2) PageSpeed Insights (PSI) — which combines CrUX data with Lighthouse lab analysis. For each metric, AuditMe checks against Google's thresholds: LCP <2.5s (good), FID <100ms (good), CLS <0.1 (good).
Example
LCP: 1.8s (Good) FID: 45ms (Good) CLS: 0.05 (Good) FCP: 1.2s (Good) TTFB: 320ms (Good)
LCP: 4.2s (Poor) FID: 250ms (Poor) CLS: 0.35 (Poor) FCP: 3.1s (Poor) TTFB: 1200ms (Poor)
Common Mistakes
- Ignoring LCP — large hero images without optimization are the #1 LCP issue
- Third-party scripts causing high FID — analytics, chat widgets, ads
- Dynamic content injection causing high CLS — ads, banners, cookie notices
- Not measuring field data — lab tests don't reflect real user experience
- Optimizing for lab scores while ignoring field data (or vice versa)
- Assuming good lab scores mean good field scores — they often differ