What is Core Web Vitals?

Core Web Vitals are a set of three specific page experience metrics that Google uses to evaluate and rank web pages based on their real-world performance for users. They were introduced as a ranking factor in June 2021 and have been progressively weighted more heavily in subsequent algorithm updates. The three metrics are: Largest Contentful Paint (LCP), which measures loading performance and specifically tracks how long it takes for the largest visible content element on the page — typically the hero image or main heading — to fully load. Google considers LCP under 2.5 seconds as 'Good', 2.5-4.0 seconds as 'Needs Improvement', and over 4.0 seconds as 'Poor'. Interaction to Next Paint (INP) replaced First Input Delay (FID) in March 2024 and measures overall page interactivity. INP captures the delay between any user interaction (click, keystroke, tap) and the next visual update on the page. INP under 200 milliseconds is 'Good', 200-500ms 'Needs Improvement', and above 500ms 'Poor'. Cumulative Layout Shift (CLS) measures visual stability — specifically how much visible content unexpectedly shifts during page load. A CLS score under 0.1 is 'Good'. This metric is commonly violated by pages that load images without defined dimensions, ads that expand after the surrounding content loads, or web fonts that cause text to reflow. These metrics are collected from real Chrome users via the Chrome User Experience Report (CrUX) dataset, not from lab tests. This means your scores reflect the actual experience of real visitors on real devices and real networks. For Next.js applications like ReddWise, optimising Core Web Vitals requires several specific techniques: using next/image for automatic image optimization, lazy loading, and proper dimension specification; implementing React Server Components to minimize client-side JavaScript bundle size; configuring font-display:swap for web fonts to prevent render-blocking; and leveraging edge network caching via Vercel or equivalent platforms to minimize global time-to-first-byte. Poor Core Web Vitals don't just hurt rankings directly — they increase bounce rates, which is an indirect ranking signal through Google's user engagement signals.