Core Web Vitals (CWV) are a set of specific factors that Google considers important in a webpage's overall user experience. They are part of Google’s broader Page Experience signals, which also include mobile-friendliness, safe-browsing, HTTPS, and intrusive interstitial guidelines. CWV focus on three aspects of the user experience: loading, interactivity, and visual stability. These are measured by three metrics: Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS).
Largest Contentful Paint (LCP) LCP measures the time it takes for the largest content element (such as an image or block of text) to become visible within the viewport, relative to when the page first started loading. A good LCP score is 2.5 seconds or less. Optimizing LCP often involves identifying the largest element and ensuring it loads quickly. This can be achieved through image optimization, using a content delivery network (CDN), or optimizing server response times.
First Input Delay (FID) FID measures the time from when a user first interacts with a page (e.g., when they click a link, tap on a button, or use a custom, JavaScript-powered control) to the time when the browser is actually able to begin processing that interaction. A good FID score is 100 milliseconds or less. Reducing FID typically involves optimizing JavaScript execution, as long JavaScript tasks can block the main thread and delay processing user input.
Cumulative Layout Shift (CLS) CLS measures the sum total of all unexpected layout shifts that occur during the entire lifespan of a page. Layout shifts usually occur when resources are loaded asynchronously or DOM elements are dynamically added to the page above existing content. A good CLS score is 0.1 or less. Preventing unexpected layout shifts involves specifying size attributes for images and videos, reserving space for ads, and inserting new content below existing content.
Why Core Web Vitals Matter for SEO Google has explicitly stated that Core Web Vitals are used in its ranking algorithm. This means that if your website provides a poor user experience, it may rank lower in search results. Websites that offer a better page experience are likely to be favored. Monitoring and improving your Core Web Vitals is an ongoing task. Google provides tools like PageSpeed Insights, Lighthouse, and the Chrome UX Report to help you measure your CWV scores and identify opportunities for improvement.
