Definition
What is Core Web Vitals?
What it is
Google introduced Core Web Vitals in 2021 as a set of measurable, user-centric performance signals. There are three metrics: Largest Contentful Paint (LCP) — the time until the page's main content (a hero image or large text block) is fully visible; target: under 2.5 seconds. Cumulative Layout Shift (CLS) — how much the layout jumps around as assets load (the button that moves just as you click it); target: under 0.1. Interaction to Next Paint (INP) — how quickly the page responds to a click or tap; target: under 200 milliseconds. Google measures these on real user devices and reports them in Search Console.
Why it matters
Core Web Vitals became a Google ranking factor in 2021. Pages that pass all three metrics get a small ranking boost; pages that fail are pushed down, particularly in mobile search. But the SEO impact is secondary to the user experience impact: a page with a 4-second LCP loses roughly 25% of its visitors before they see any content, according to Google's own research. WordPress sites with page builders routinely fail LCP. Next.js sites deployed on Vercel's CDN typically pass all three without extra configuration.
When you need it
You need to fix Core Web Vitals when your Search Console shows 'Poor' URLs, your Lighthouse mobile score is below 70, or your site has a high bounce rate. Common culprits: large unoptimised images, render-blocking third-party scripts, Google Fonts loading synchronously, and layout shifts caused by ads or embeds.
Source: Google Web.dev — Core Web Vitals
People Also Ask
- How do I check my Core Web Vitals score?
- Open Google Search Console → Experience → Core Web Vitals. This shows real-user data from the past 28 days, broken down by mobile and desktop. You can also run a Lighthouse audit in Chrome DevTools for a lab-based estimate.
- What causes a slow Largest Contentful Paint (LCP)?
- Usually: a large unoptimised hero image, a render-blocking CSS file, a slow server response, or a third-party font loading synchronously. Next.js handles image optimisation, font loading, and CDN delivery automatically — which is why it scores well out of the box.
- Do Core Web Vitals affect SEO rankings?
- Yes, directly. Google confirmed CWV as a ranking signal in 2021. The impact is a tiebreaker rather than a dominant factor — very relevant content can outrank a faster competitor — but for competitive queries, passing CWV gives you an edge.
- Can a WordPress site pass Core Web Vitals?
- Yes, with effort. Switching to a lightweight theme, optimising images with ShortPixel or Imagify, using Cloudflare or Bunny CDN, removing unnecessary plugins, and deferring scripts can push most WordPress sites to a pass. Headless WordPress or a full Next.js rebuild is a cleaner long-term solution.
- Is Interaction to Next Paint (INP) harder to pass than the old First Input Delay (FID)?
- Yes. INP (introduced as the permanent metric in 2024) measures all interactions throughout the page session, not just the first one. Sites with heavy JavaScript frameworks or complex UI interactions that previously passed FID often fail INP. Next.js's React Server Components help by shipping less JavaScript to the browser.