Core Web Vitals are a set of user-centric performance metrics introduced by Google to measure the user experience of a website. These metrics are designed to evaluate the speed, responsiveness, and visual stability of a website. There are three Core Web Vitals:

  1. Largest Contentful Paint (LCP): This metric measures the loading speed of the largest content element on the screen, such as an image or video. Google recommends that the LCP should occur within 2.5 seconds of when the page starts loading.

  2. First Input Delay (FID): This metric measures the time it takes for the website to respond to the user's first interaction, such as clicking a button or filling out a form. Google recommends that the FID should be less than 100 milliseconds.

  3. Cumulative Layout Shift (CLS): This metric measures the visual stability of the page, particularly with regard to how much the content shifts around as the page loads. Google recommends that the CLS score should be less than 0.1.

Google has announced that these Core Web Vitals will become a ranking factor for websites in May 2021, meaning that websites with better Core Web Vital scores are likely to rank higher in Google search results. Therefore, website owners and developers are encouraged to optimize their websites to meet these metrics.