Understanding Core Web Vitals

Core Web Vitals are Google's attempt to measure real-world user experience rather than abstract technical benchmarks. Here's what each metric actually captures.

LCP — Largest Contentful Paint

LCP measures how long it takes for the largest visible element on the page (often a hero image or heading) to render. Slow LCP is usually caused by large unoptimised images, slow server response times, or render-blocking resources loading before the main content.

CLS — Cumulative Layout Shift

CLS measures visual stability — how much content unexpectedly shifts around as a page loads. The classic example is text jumping down the page because an image above it just finished loading without reserved space. Setting explicit width and height attributes on images and embeds largely solves this.

INP — Interaction to Next Paint

INP measures how responsive a page feels when someone actually interacts with it — clicking a button, opening a menu. Heavy JavaScript execution is the usual culprit here; breaking up long-running scripts and deferring non-critical JavaScript both help.

Why These Numbers Matter Beyond SEO

Core Web Vitals are a ranking signal, but they're also a genuine proxy for whether visitors have a good experience on your site — which is worth optimising for on its own merits, independent of any SEO benefit.

Where To Start

Image optimisation and fast, stable server infrastructure address LCP and CLS for most sites. INP usually needs a closer look at what JavaScript is running and when.