Glossary · performance
Core Web Vitals
Definition
Core Web Vitals are Google's 3 main web performance metrics defined in 2020: LCP (Largest Contentful Paint), CLS (Cumulative Layout Shift), INP (Interaction to Next Paint). Google ranking factor; good scores deliver 10-30% SEO advantage.
Detailed explanation
LCP (Largest Contentful Paint): time for the page's largest content element to render. Targets: <2.5s 'good', 2.5-4s 'needs improvement', >4s 'poor'. Reduced via image optimization + edge CDN + critical CSS.
CLS (Cumulative Layout Shift): amount of layout shift during page load. Target: <0.1 'good'. Zero out via image dimensions, font fallback, reserved space for dynamic content.
INP (Interaction to Next Paint): replaced FID in 2024. UI response time after user click/type. Target: <200ms 'good'. Lowered via heavy JS chunk splitting + main-thread optimization.
Tools: Google PageSpeed Insights, Search Console (Core Web Vitals report), Web Vitals Chrome extension, real-user monitoring (Sentry, Datadog).
Use cases
→Google ranking optimization
→E-commerce conversion lift
→Performance budget setting
→User experience improvement
Pros
- +Google ranking factor (SEO advantage)
- +10-30% conversion rate lift
- +20-40% bounce rate reduction
- +Speed is measurable + optimizable
Cons
- −Optimization is ongoing (new features can break LCP)
- −3rd-party scripts (analytics, chat) hurt scores
- −Mobile vs desktop need separate optimization
Related terms
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