Technical SEO
Core Web Vitals Explained for Non-Developers
What LCP, INP and CLS measure, where to check them for free and which fixes to ask your developer or builder for.
By the Seozumi editorial team · · about 5 min read
Core Web Vitals are three measurements Google uses to describe how a page feels to real visitors: how fast the main content appears, how quickly it responds to taps and clicks, and whether the layout jumps around. They are part of Google’s page experience signals. Good scores will not make a weak page rank, but very slow or unstable pages frustrate visitors and can lose out to similar pages that work better.
The three metrics in plain English
| Metric | What it measures | “Good” threshold |
|---|---|---|
| LCP — Largest Contentful Paint | How long until the biggest visible element (often a hero image or headline) appears | 2.5 seconds or less |
| INP — Interaction to Next Paint | How quickly the page visibly responds after a tap, click or key press | 200 milliseconds or less |
| CLS — Cumulative Layout Shift | How much content moves unexpectedly while the page loads | 0.1 or less |
Google assesses these at the 75th percentile of real visits, split by mobile and desktop. Thresholds come from Google’s Core Web Vitals documentation.
Field data versus lab data
Field data comes from real Chrome users visiting your site (the Chrome UX Report). It is what Google uses for page experience. Lab data is a simulated test on one device and connection. Lab tests are great for debugging but can differ a lot from what visitors experience. New or low-traffic sites often have no field data at all; in that case, use lab data as a guide.
Where to check your scores for free
- PageSpeed Insights: enter a URL to see field data (if available) and a lab test with suggestions.
- Google Search Console → Core Web Vitals report: groups of URLs rated Good, Needs improvement or Poor, based on field data.
- Chrome DevTools → Lighthouse and Performance panels, for detailed debugging.
Fixes that usually help LCP
- Compress and resize the hero image; serve WebP or AVIF where your platform supports it. See our image SEO guide.
- Do not lazy-load the main hero image; lazy-load images further down instead.
- Reduce slow server response: good hosting, caching and a CDN.
- Remove render-blocking scripts and unused CSS from the top of the page.
- Limit heavy sliders and auto-playing videos above the fold.
Fixes that usually help INP
- Remove third-party scripts you no longer use: old chat widgets, duplicate analytics, abandoned A/B testing tools.
- Delay non-essential scripts until after the page is interactive.
- Ask your developer to break up long JavaScript tasks and avoid heavy work on every click.
- On page builders, reduce animations and very large pages with hundreds of widgets.
Fixes that usually help CLS
- Set width and height (or aspect-ratio) on images, videos and embeds so space is reserved.
- Reserve space for cookie banners and ads instead of pushing content down.
- Load web fonts in a way that avoids big size changes (for example
font-display: swapwith a similar fallback font). - Do not insert content above existing content after load unless the user asked for it.
A practical order of work
- Check the Core Web Vitals report in Search Console to find which URL groups are Poor on mobile.
- Pick a representative URL from the worst group and run it in PageSpeed Insights.
- Fix the issue affecting the most pages first, often a shared template, header image or script.
- After deploying, use “Validate fix” in Search Console. Field data is collected over 28 days, so improvements take weeks to show.
What not to worry about
Chasing a perfect 100 lab score is rarely worth it. Focus on passing the thresholds for real users, and on content that answers the visitor’s question. If you are choosing what to spend time on this month, a useful new page or an updated old post often matters more than shaving milliseconds off an already “Good” page.
