Core Web Vitals: definition
Core Web Vitals are a set of metrics defined by Google to measure a page's real-world experience as perceived by a visitor: loading speed, visual stability and responsiveness.
The three metrics behind Core Web Vitals
LCP (Largest Contentful Paint) measures how long it takes to render the largest visible element on screen, often a product image or a main banner. CLS (Cumulative Layout Shift) measures visual stability: it quantifies unexpected element movement during loading, for example when a banner pushes content downward after the fact. INP (Interaction to Next Paint), which replaced FID in 2024, measures response time to a visitor interaction, such as clicking Add to cart.
These metrics are measured by Google on real traffic through the Chrome User Experience Report, viewable in particular via PageSpeed Insights. For a PrestaShop or WooCommerce shop, they matter twice over: they reflect the buying experience, and Google uses them as one signal among others in its ranking.
Each metric has published thresholds from Google (good, needs improvement, poor), which makes it possible to prioritise fixes rather than optimise vaguely.
Frequently asked questions
Are Core Web Vitals a decisive ranking factor on Google?
Where can you check the Core Web Vitals of a particular shop?
Does a good PageSpeed Insights score guarantee good Core Web Vitals?
Describe your need in one minute
A few targeted questions so I can reply with an estimate rather than another questionnaire.