When a developer says your site "fails Core Web Vitals", they mean it falls short on three measures Google uses to judge how a page feels to a real visitor. Here is each one without the jargon.
What are the three Core Web Vitals?
| Metric | What it measures | Good score |
|---|---|---|
| LCP — Largest Contentful Paint | How long until the main content (usually the big image or headline) appears | 2.5 seconds or less |
| INP — Interaction to Next Paint | How quickly the page reacts when someone taps or clicks | 200 milliseconds or less |
| CLS — Cumulative Layout Shift | How much the page jumps around while loading | 0.1 or less |
Google measures these on real visitors' phones and laptops, and judges a page on how most of its visitors experience it.
Do Core Web Vitals affect ranking?
Yes, but as one signal among many. A fast page with thin content won't outrank a slower page that answers the question far better. Where two pages are otherwise similar, the better experience can tip it. The more reliable benefit is simpler: slow pages lose visitors before they ever read a word.
Why do websites fail them?
- Slow LCP: large uncompressed images, a slow server, fonts or scripts that block the page from showing, or heavy animation that holds the first paint back.
- Poor INP: too much JavaScript running on the page, often from tracking, chat widgets and plugins.
- High CLS: images and ads without a set size, so the text moves when they load; late-loading fonts that change the text size.
Website makers and big themes tend to load the same scripts on every page, which is why they struggle on mobile. We explain that trade-off in website builder vs web designer.
How do you check yours?
- Open PageSpeed Insights and enter your address.
- Look at the field data at the top — real-visitor results, when your site has enough traffic — before the lab score below it.
- In Google Search Console, the Core Web Vitals report groups your URLs into good, needs improvement and poor.
A lab score from a single test can swing a lot between runs and between machines, so test a few times and treat the field data as the real answer.
The quickest fixes
- Resize and compress images, and use modern formats (WebP or AVIF).
- Set a width and height on every image and video.
- Load only the scripts each page needs, and delay the rest.
- Host fonts with the site and limit how many you use.
- Remove plugins and embeds you don't use.
Performance is part of every build we do — see our web development service — and the launch checklist covers it before go-live.