What are Core Web Vitals, and do they affect SEO?

The thresholds come from Google's web.dev documentation. They are measured on real visits, not only in lab tests: a page passes when at least three in four visits meet each 'good' threshold, counted separately for mobile and desktop.

Google says Core Web Vitals are used by its ranking systems, and also that Google Search always seeks to show the most relevant content, even if the page experience is sub-par. In practice, Core Web Vitals tend to matter in close contests, and they affect conversions directly: slow, jumpy pages lose visitors.

Common fixes:

• LCP: compress and correctly size the main image, preload it, and reduce server response time and render-blocking scripts.
• INP: break up long JavaScript tasks and cut third-party scripts such as tag managers, chat widgets and testing tools.
• CLS: set width and height on images and embeds, and reserve space for banners and ads.

Check your field data in Search Console's Core Web Vitals report or PageSpeed Insights before optimising, so you fix the templates that real users struggle with rather than chasing a lab score.