What Are Core Web Vitals and Why Do They Matter for SEO?

Core Web Vitals are a set of performance metrics that Google uses to measure the quality of a user's experience on a web page. They became a confirmed ranking factor in 2021 and are assessed for every page on your website. A page that loads slowly, responds sluggishly to clicks or shifts its layout around as it loads will score poorly — and may rank below faster, better-experience competitors.

The metrics are technical, but the underlying idea is simple: Google wants to rank pages that are actually pleasant to use on real devices in real conditions. Understanding what each metric measures helps you prioritise improvements and work effectively with developers.

The three Core Web Vitals metrics

Largest Contentful Paint (LCP) measures how quickly the largest visible element on the page — usually the hero image or main heading — loads and becomes visible to the user. A good LCP is under 2.5 seconds. Slow LCP is most commonly caused by large unoptimised images, slow server response times, or render-blocking resources (CSS and JavaScript files that delay page rendering).

Interaction to Next Paint (INP) measures how quickly the page responds to a user's first interaction — clicking a button, opening a menu, tapping a link. A good INP is under 200 milliseconds. Poor INP is usually caused by heavy JavaScript that keeps the browser's main thread busy and unable to respond quickly to user input. Cumulative Layout Shift (CLS) measures visual stability — how much content moves around unexpectedly as the page loads. A good CLS score is under 0.1. Common causes include images without specified dimensions, fonts that load late and cause text to reflow, and banners or embeds that load after the surrounding content.

How to check your Core Web Vitals scores

Google Search Console's Core Web Vitals report shows field data — real measurements from Chrome users visiting your pages — grouped into Good, Needs Improvement and Poor. This is the most authoritative source because it reflects actual user experiences rather than synthetic lab tests. The report flags pages with poor scores and links to PageSpeed Insights for detail on the specific issues.

PageSpeed Insights (pagespeed.web.dev) provides both field data and a lab-based audit of any URL. It shows a score out of 100 and a detailed list of opportunities to improve performance, with estimated time savings for each fix. Lighthouse in Chrome DevTools runs the same audit locally, useful for testing changes before deploying them to a live site.

Fixing common Core Web Vitals problems

For LCP improvements, start with images: ensure every large image is properly compressed and served in a modern format (WebP), that images have explicit width and height attributes in HTML to avoid layout shifts, and that the hero image is preloaded in the HTML head. Slow server response times require either a faster hosting plan or a content delivery network (CDN) to serve cached pages from locations closer to users.

For CLS improvements, specify explicit dimensions for every image and video, avoid injecting content above existing content after load, and use CSS font-display settings to prevent font-loading layout shifts. Most website platforms have plugins or built-in settings that handle these automatically — WordPress users can address many Core Web Vitals issues through a performance plugin like WP Rocket or Perfmatters without custom development.