Core Web Vitals: what they are and how to improve them

Core Web Vitals are three metrics Google uses to measure the real experience on a page. Not simulations: data collected from real people, on real devices.

A website can have great content and careful design. If it’s slow, unstable or doesn’t respond straight away, much of that work is lost. People leave, Google notices, rankings suffer. That’s why it isn’t a topic to leave to developers alone.

The three metrics

LCP, Largest Contentful Paint

How long it takes for the main content of the page to become visible. Good within 2.5 seconds; over 4 seconds is “poor”.

INP, Interaction to Next Paint

How responsive the site is: the time between a tap or click and the page’s visible reaction. Good under 200 milliseconds; over 500 is a problem.

CLS, Cumulative Layout Shift

How much the page “jumps” while loading: buttons moving, text changing place. Good under 0.1.

Three numbers, but behind each one is a simple question. Does the page load quickly? Do the buttons respond straight away? Does the page stay still under your fingers?

Why they matter for business

• Experience. A fast, stable site shows care without saying a word. A slow one says the opposite, even if the service is excellent.
• Rankings. They’re one of the signals Google uses to judge a page. Not the only one, but among sites with similar content they can make the difference.
• Conversions. The slower the page, the more people give up. Fewer people staying means fewer enquiries, fewer bookings, fewer sales.

The most common problems

• Unoptimised images. Files of several megabytes, uncompressed and not in modern formats like WebP or AVIF.
• Too much JavaScript. Plugins, tracking scripts and third-party widgets that block the page.
• Slow hosting. If the server takes too long just to respond, no optimisation on the site is enough.
• Unstable layout. Images without dimensions, fonts loading late, banners appearing afterwards.

Google Search Console shows how your site is doing, page by page, split into “good”, “needs improvement” and “poor”. It’s free, and it’s the first place to look.

How to improve them

For LCP

• compress images and use modern formats, with deferred loading where it makes sense;
• preload critical resources;
• choose hosting that responds quickly.

For INP

• reduce and defer unnecessary JavaScript;
• avoid long tasks that block the browser;
• limit third-party scripts and widgets.

For CLS

• always give images and video a width and height;
• don’t insert content above what’s already visible;
• load fonts so they don’t shift the text.

It’s one of the reasons we build websites in Astro: it produces light HTML pages with no unnecessary JavaScript, and starts with Core Web Vitals already on the right side. This website is an example.

The point

Core Web Vitals aren’t an optimisation to do “when there’s time”. They measure how well your site works for the people using it. A site that meets them is faster, more stable, more credible, and converts better.

If you want to know where yours stands, start from Search Console. If you need someone to read the data and act on it, write to us.