Core Web Vitals are 3 technical metrics Google uses to assess your site's user experience. Since they were folded into the algorithm in 2021, a poor score can cost you positions even if your content is excellent. It is the first time Google has made user experience an official ranking criterion.
The 3 metrics Google measures
- LCP (Largest Contentful Paint): the loading time of the largest visible element. Target: under 2.5 seconds.
- INP (Interaction to Next Paint): responsiveness to clicks and input. Target: under 200 ms.
- CLS (Cumulative Layout Shift): visual stability during loading. Target: a score below 0.1.
These 3 metrics measure what your visitor feels, not what Google reads. A good Core Web Vitals score is a promise of comfortable browsing. It is also a direct signal towards better positioning.
LCP: load the essentials in under 2.5 seconds
LCP measures how long it takes to display the largest element visible at first glance: the hero image, the H1 heading or the main block. Above 2.5 seconds, Google considers your loading slow. Above 4 seconds, it is judged poor and penalises your ranking.
The most frequent causes of a poor LCP: uncompressed images, slow hosting, no browser caching. To diagnose, start with PageSpeed Insights (free), which gives you a precise score and the fixes to prioritise. The complete documentation on LCP is available on web.dev with code examples for each type of fix.
INP and CLS: responsiveness and visual stability
INP replaced the old FID metric in March 2024. It measures the delay between your visitor's action (a click, typing into a form) and the page's visible response. CLS measures how much your page jumps during loading, when images or advertisements appear late and shift the text.
To fix CLS: always set explicit dimensions (width and height) on your images and iframes. An img tag with no reserved dimensions creates a layout jump on every load. It is the quickest and most effective fix.
To analyse INP and CLS in detail, two free tools stand out: Lighthouse (built into Chrome DevTools, Performance tab) and WebPageTest. Both simulate real visits and tell you exactly which element triggers the problem.
Tracking your Core Web Vitals with Google Search Console
Google Search Console includes a Core Web Vitals report in your dashboard. It lists your URLs classified as red (poor), amber (needs improvement) or green (good), from your visitors' real field data. It is the most reliable source, far more so than laboratory tests.
- Check the Core Web Vitals report in Search Console at least once a month
- Fix the URLs classified as Poor (red score) first
- Run a PageSpeed Insights audit on your key pages: home, services, contact
- Request revalidation in Search Console after each major fix
- Watch for regressions after every update to your site or its plugins
The priority fixes for a small company
Compress your images to WebP (150 to 200 KB maximum for a hero), switch on browser caching, use fast hosting, and load your fonts with font-display: swap. Those 4 actions cover 80% of the possible gains on LCP. For CLS, add fixed dimensions to every image.
To go further in auditing your performance, Screaming Frog crawls your whole site and identifies the slowest pages. Semrush offers a complete site audit that includes Core Web Vitals with recommendations prioritised by expected SEO impact.
Core Web Vitals are a technical pillar of SEO, but they do not do the job alone. To build a complete strategy combining technique and content, read the basics of SEO for freelancers and start with the fundamentals before going into technical detail.