Core Web Vitals – Definition

Core Web Vitals are metrics defined by Google to measure the user experience of a web page: Largest Contentful Paint (LCP), Cumulative Layout Shift (CLS), and Interaction to Next Paint (INP).

Core Web Vitals have been a Google ranking factor since 2021. Particularly relevant for e-commerce pages are: LCP (how fast does the largest visible element load — often the hero image?) and CLS (how much do elements shift during load — issues usually stem from images without defined dimensions?). CMS systems directly influence Core Web Vitals through image optimization, preloading, server-side rendering, and avoiding layout shifts via correct `width`/`height` attributes. Interaction to Next Paint (INP), which replaced First Input Delay as the third Core Web Vital in 2024, measures how responsive a page feels to real interactions throughout its entire lifecycle, making it particularly sensitive to heavy client-side JavaScript that blocks the main thread — a common issue on pages loaded with tracking scripts and personalization tags running simultaneously. Because Core Web Vitals are measured from real user data rather than synthetic lab tests, a page can pass internal checks and still fail assessment if visitors on slower devices experience it differently.