If you have ever run your website through Google PageSpeed Insights, you’ve seen the scores. Green is good, red is bad, and somewhere in between there are three acronyms — LCP, INP, and CLS — that most people gloss over without fully understanding.
These three metrics are Google’s Core Web Vitals: the specific measurements it uses to judge whether your website actually feels good to use. They’re baked into Google’s ranking algorithm, and improving them can directly improve your search visibility as well as how visitors experience your site.
Here’s what each one means in plain terms, and what actually moves the needle.
LCP — Largest Contentful Paint
LCP measures how long it takes for the biggest visible element on your page to load. This is usually your hero image, a large heading, or a banner. Google considers anything under 2.5 seconds to be good.
The biggest culprits are:
- Unoptimised hero images — large JPEGs that haven’t been compressed or converted to WebP
- No preload hint — the browser doesn’t know to fetch the image early
- Slow server response — if your hosting is sluggish, everything downstream suffers
- Render-blocking resources — CSS or JavaScript that delays the page from starting to render
The fix usually involves compressing and properly sizing images, adding a <link rel="preload"> for the hero image, and ensuring your hosting has solid response times.
INP — Interaction to Next Paint
INP replaced FID (First Input Delay) as a Core Web Vital in 2024. It measures how responsive your page feels when a user interacts with it — clicking a button, opening a menu, submitting a form. Google wants this under 200 milliseconds.
Poor INP scores are typically caused by:
- Heavy JavaScript that blocks the browser’s main thread
- Too many plugins on WordPress sites, each adding their own scripts
- Third-party trackers and analytics firing on every interaction
- Unoptimised event listeners that trigger expensive operations
Improving INP often means auditing what JavaScript is actually running on your pages. On WordPress sites, disabling unused plugins and deferring non-critical scripts can make a significant difference.
CLS — Cumulative Layout Shift
CLS measures how much the page layout shifts around as it loads. You’ve experienced bad CLS when you try to tap a button and it jumps just as your finger lands — and you end up clicking something else entirely. Google wants a CLS score under 0.1.
Common causes:
- Images without dimensions — the browser doesn’t know how much space to reserve, so content shifts when the image loads
- Fonts swapping in — if a system font loads first and then your custom font replaces it, text can reflow and push other elements around
- Ads and embeds that inject themselves into the page after it has already rendered
Fixing CLS is often about discipline: always specify width and height attributes on images, use font-display: swap carefully, and reserve space for dynamic content.
How to check your scores
The easiest way is Google PageSpeed Insights. Paste in your URL and you’ll see your real-world Core Web Vitals scores alongside a lab-based performance score. Pay attention to the Field Data section — that’s based on actual visits to your site, not a simulated test.
You can also find Core Web Vitals data in Google Search Console under Experience > Core Web Vitals. This shows you which pages are failing and by how much.
What to do if your scores are poor
Start with the data. PageSpeed Insights tells you exactly what it found — use the Opportunities and Diagnostics sections as your to-do list. The issues flagged there are ranked by impact, so fix the biggest ones first.
For most WordPress sites, the biggest wins come from image optimisation, reducing plugin count, and switching to a faster host or enabling proper caching. For custom-built sites, JavaScript weight and rendering strategy tend to be the key levers.
Core Web Vitals aren’t a one-time fix — they’re something to revisit regularly, especially after adding new features, plugins, or third-party integrations.
If you want an honest assessment of where your site stands, we’re happy to take a look.