Core Web Vitals are three metrics Google uses to measure the real quality of the user experience on a web page. These aren’t lab simulations—they are data collected from real users, on real devices, in real conditions.
A site can have excellent content, a polished design, and a solid offer. If it is slow, unstable, or unresponsive, much of the work done upstream is wasted. People leave. Google records it. Rankings suffer.
That’s why Core Web Vitals are not a topic to be left only to developers.
What Core Web Vitals Measure
The three main metrics are:
LCP — Largest Contentful Paint
Measures how long it takes for the main content of the page to become visible. Google considers a value within 2.5 seconds as good. Beyond 4 seconds, the site is classified as “poor.”
INP — Interaction to Next Paint
Measures the site’s responsiveness: the time between a user interaction (click, tap, key press) and the visible response of the page. Below 200 ms is good. Above 500 ms is a problem.
CLS — Cumulative Layout Shift
Measures visual stability during loading. How many times the page “jumps” while loading—buttons moving, text shifting position. A good value is below 0.1.
Three numbers. But behind each one is a concrete user experience: does the page load quickly? Do the buttons work immediately? Does the page stay still under your fingers?
Why They Impact Business
- User Experience. A fast and stable site communicates professionalism without saying a word. A slow or jumpy site does the opposite—even if the product or service offered is excellent.
- Google Ranking. Core Web Vitals are one of the signals Google uses to evaluate page quality. They aren’t the only factor, but in competitive niches—where multiple sites offer similar content—they can make the difference between the first and second page.
- Conversions. Real data: as loading time increases, so does the bounce rate. A page that takes 5 seconds to load loses a significant portion of users compared to one that takes 2 seconds. Fewer users staying means fewer forms filled out, fewer purchases, fewer contacts.
Common Issues
Most sites have problems that impact Core Web Vitals for very concrete reasons:
- Unoptimized Images. 3–5 MB files served without compression or modern formats (WebP, AVIF) directly slow down LCP.
- Excessive JavaScript. Plugins, tracking scripts, and third-party widgets that block page rendering and increase INP.
- Slow Hosting. A server that takes 800 ms just to respond is a structural problem that no frontend optimization can fully resolve.
- Unstable Layout. Images without defined dimensions, fonts loading late, banners appearing after initial load—all contribute to CLS.
Google Search Console shows this situation in detail, classifying site URLs as “Good,” “Needs Improvement,” or “Poor” based on real user data. It’s a free tool that is worth reading before any other intervention.
How to Improve Core Web Vitals
There is no universal solution, but some interventions have a direct and measurable impact:
For LCP:
- Optimize images (compression, modern formats, correct lazy loading)
- Preload critical resources with
<link rel="preload"> - Use hosting with low response times (TTFB below 200 ms)
For INP:
- Reduce and postpone unnecessary JavaScript
- Avoid long tasks on the browser’s main thread
- Minimize third-party dependencies
For CLS:
- Always define
widthandheightfor images and videos - Avoid dynamically inserted content above the fold
- Load fonts with
font-display: swap
At MarfCode, we use Astro for static sites and SvelteKit for web apps for this very reason: Astro generates pure HTML with zero superfluous JavaScript, which translates to structurally better Core Web Vitals compared to any solution based on WordPress with multiple theme builders and plugins.
The Bottom Line
Core Web Vitals are not an optional optimization to be done “when there is time.” They are a direct measure of how well your site works for the people who use it.
A site that meets them is faster, more stable, more credible—and has a better chance of converting visitors into customers. A site that ignores them loses on all three fronts: user experience, organic visibility, and conversions.
If you want to know where your site stands on these metrics, the starting point is Google Search Console. If you need someone to interpret the data and intervene concretely, we are here.
