What are Core Web Vitals and why do they matter?
Core Web Vitals are three metrics from Google that measure how fast and smoothly your website loads from the visitor’s perspective: how quickly the main content appears, how fast the site responds to a click, and how stable the layout is while loading. They matter because they directly affect whether a visitor stays or leaves — and because Google takes them into account when ranking pages.
The three metrics you need to know
LCP (Largest Contentful Paint) measures how long it takes for the largest element on screen to appear — typically the main image or heading. The target is under 2.5 seconds. If a visitor stares at a blank screen longer, some leave before the site even shows up.
INP (Interaction to Next Paint) measures how quickly the site responds when you click or tap something. The target is under 200 milliseconds. A slow response makes the site feel like it’s “freezing” and frustrates users even on an otherwise fast page.
CLS (Cumulative Layout Shift) measures how much the content “jumps” while loading. The target is under 0.1. When a button shifts just as you go to click it, that’s exactly what CLS penalises.
What most often slows a website down
Most speed problems come from a few recurring things: huge unoptimised images, dozens of plugins and third-party scripts, heavy themes that load code even for features you don’t use, and missing image dimensions that make content jump. Each of these can be addressed — some easily, others requiring changes to the site’s foundations.
How to improve Core Web Vitals
Practical steps, from the most effective:
- Optimise images. Use modern formats (WebP, AVIF), correct dimensions and lazy loading for images below the fold.
- Cut third-party scripts. Every chat widget, analytics script or ad code slows the site. Keep only the ones you truly need.
- Choose fast technology. Static generation (for example on Astro) sends only the bare minimum to the browser, so the site is fast by its very nature.
- Reserve space for content. Specify image dimensions and set aside room for elements that load later, so nothing jumps.
Speed isn’t just for Google
It’s easy to treat Core Web Vitals as another SEO checklist item. In reality, speed is mostly about people. Every extra second of loading raises the bounce rate and lowers the number of completed purchases and enquiries. A fast site sells better — and good search rankings are just a pleasant bonus on top.
