Site performance is very important, first of all, from the perspective of users, who expect a good experience when visiting the site. The user should not wait too long for the page to load. We all know how annoying it can be when we want to press an element and it jumps to another place on the page or when we click on a button and then nothing happens for a very long time. The state of a site’s performance in these aspects is measured by Web Vitals performance metrics and most importantly by a set of three major Core Web Vitals metrics (LCP — Largest Contentful Paint, CLS — Cumulative Layout Shift, INP — Interaction to Next Paint). They are responsible for measuring the 3 things: loading time, visual stability and interactivity. These metrics are also important for the websites themselves because, in addition to the user experience, they are also taken into account in terms of the website’s positioning in search engines (SEO), which is crucial for most websites on the Internet, Allegro included.