Core Web Vitals
Google's standardised metrics measuring real-world user experience: loading speed, responsiveness, and visual stability.
The three Core Web Vitals
Largest Contentful Paint (LCP) measures loading performance. It tracks when the largest content element becomes visible—typically a hero image or heading. Good LCP is under 2.5 seconds. Slow LCP means visitors stare at loading screens.
Interaction to Next Paint (INP) measures responsiveness. When someone clicks a button or types in a form, how quickly does the page react? Good INP is under 200 milliseconds. Laggy interactions frustrate users and signal performance problems.
Cumulative Layout Shift (CLS) measures visual stability. Have you visited a site where content suddenly jumps as images load, causing you to click the wrong link? That's layout shift. Good CLS is under 0.1. Stable layouts feel professional and prevent user errors.
Why Core Web Vitals matter
Google uses Core Web Vitals as ranking signals. Sites with poor vitals score lower in search results, regardless of content quality. This makes technical performance directly impact visibility.
Beyond SEO, Core Web Vitals correlate strongly with conversion rates and user satisfaction. Fast, responsive, stable sites convert better because they respect visitors' time and don't frustrate them with jank.
Measuring Core Web Vitals
Google Search Console reports real-world Core Web Vitals data from actual visitors. Chrome DevTools and PageSpeed Insights provide lab testing. Both perspectives matter—lab data helps diagnose problems, field data shows real user experience.
Metrics are scored green (good), yellow (needs improvement), or red (poor) based on the 75th percentile of user experiences. To pass, 75% of page visits must meet the "good" threshold for each metric.
Achieving excellent Core Web Vitals
Building with Astro provides a massive advantage—static HTML loads instantly, minimal JavaScript means fast interactivity, and component architecture prevents layout shifts. Optimised images, edge hosting, and thoughtful design complete the picture.
Every Fernside site targets green scores across all three metrics. We measure vitals during development, fix issues before launch, and monitor ongoing performance to maintain excellent user experience.
Related terms
Why it matters
Understanding “Core Web Vitals” helps you speak the same language as our design and development team. If you need help applying it to your project, book a Fernside call.