Website speed
Core Web Vitals, explained in plain English
Core Web Vitals are three measurements Google uses to describe how a page feels to a real visitor. The names are technical, but the ideas are simple: how fast does the page appear, how quickly does it respond, and does it jump around while loading?
LCP: how fast the main content appears
Largest Contentful Paint measures how long it takes for the biggest thing on the screen, usually a main image or a large heading, to show up. Google considers 2.5 seconds or less good, and over 4 seconds poor.
The usual fixes are smaller, correctly sized images, a faster server, and removing code that blocks the page from drawing.
INP: how quickly the page reacts
Interaction to Next Paint measures the delay between a tap or a click and the page visibly responding. It replaced an older measure called First Input Delay in 2024. Good is 200 milliseconds or less, and over 500 milliseconds is poor.
Pages feel sluggish here when too much JavaScript is running. Fixes include removing scripts you don't need, loading others later, and keeping heavy work off the moment a visitor taps something.
CLS: whether the page jumps around
Cumulative Layout Shift measures unexpected movement as the page loads. You've seen it: you're about to tap a button and an ad loads above it, so everything shifts down. A score of 0.1 or less is good, and over 0.25 is poor.
The usual fixes are giving images and embeds a set size, reserving space for ads and banners, and loading fonts carefully.
How to check yours
PageSpeed Insights shows all three for a URL, including real-world data from visitors when there's enough traffic. Google Search Console has a Core Web Vitals report that groups your pages by how they perform. Test on mobile first, because that's where most problems show.
How much do they matter?
They're one signal among many, and good content still matters most. But they're also a fair measure of whether your site is pleasant to use, and that affects whether visitors stay and get in touch. I treat them as a checklist for quality, not a number to obsess over.
A simple order of work
- Measure your key pages on mobile and write down the three scores.
- Fix the biggest images first, since they usually decide how fast the main content appears.
- Remove scripts you don't use, and delay the ones that can wait.
- Give images, ads and embeds a fixed size so nothing jumps while the page loads.
- Test again on a real phone, not only in a tool.
Myths worth ignoring
- You need a score of 100. You don't. Passing all three vitals matters more than a perfect number.
- Core Web Vitals decide your ranking on their own. They're one signal among many, and relevant content still matters most.
- Desktop results tell you enough. Most visitors are on phones, and mobile is where problems show up.
What to ask a developer who offers to fix them
- Which of the three is failing on my site, and on which pages?
- What will you change, and how will we measure the result?
- Will you show me before and after numbers from the same test?
- Will the improvement last when I add new pages and images, or will it slip back?