Understanding Core Web Vitals

Why Core Web Vitals Matter

You’ve probably been there: you’ve compressed some images, enabled caching, maybe even switched to a faster host… yet the site still doesn’t feel fast. And in Google Search Console you keep seeing warnings about Core Web Vitals. That’s usually the moment the real question appears: what exactly do I need to fix?

Google has been trying for years to measure user experience with concrete metrics instead of vague feelings. Core Web Vitals are basically that common language: three signals that tell Google how your page feels to users in three critical moments — when it loads, when they interact, and when things unexpectedly move around on the screen.

Put simply: Core Web Vitals form the bridge between UX and SEO. The better these metrics are, the happier your users are — and the more competitive you are in search.

What Are Core Web Vitals?

Right now, Google focuses on three main metrics as Core Web Vitals:

LCP – Largest Contentful Paint: how quickly the main content of the page becomes visible.
INP – Interaction to Next Paint: how quickly the page responds when a user interacts (clicks, taps, types).
CLS – Cumulative Layout Shift: how much the layout jumps around unexpectedly while the page loads.

These metrics are based not only on lab tests but also on real user data from Chrome (field data). That’s why numbers can differ slightly between tools, but the overall pattern is what matters.

1. LCP – How Fast Does the “Real Page” Appear?

LCP answers a simple question: how long does it take until the user sees the most important part of the page — usually a hero image, large banner, or main content block. Users don’t care if every tiny asset is fully loaded. They care about when they feel, “Okay, the page is here.”

As a rule of thumb:

Good LCP: ≤ 2.5 seconds
Needs improvement: 2.5–4 seconds
Poor: > 4 seconds

Common causes of poor LCP:

Very large, unoptimised hero images.
Slow server responses and high TTFB.
Blocking CSS and JavaScript that must load before content appears.
Heavy web fonts or third-party scripts that delay rendering.

Practical ways to improve LCP:

Compress and resize images properly; use modern formats like WebP where possible.
Use a CDN and optimise server response time.
Inline or prioritise critical CSS and defer non-critical CSS and JS.
Preload key resources such as the main hero image and primary web fonts.

2. INP – How Responsive Is Your Page to User Actions?

Previously, Google used FID (First Input Delay), which only measured the first interaction. Now INP has replaced it and looks at responsiveness across the whole lifetime of the page: how long users wait after they click, tap, or type before something actually happens.

Rough thresholds for INP:

Good INP: ≤ 200 ms
Needs improvement: 200–500 ms
Poor: > 500 ms

Typical causes of poor INP:

Too much heavy JavaScript running on the main thread.
Long tasks (>50 ms) that block user interactions.
Multiple third-party scripts (chat widgets, analytics, tags) loading and executing at the same time.

Practical ways to improve INP:

Break up long-running JavaScript tasks into smaller chunks.
Defer or lazy load non-critical third-party scripts.
Remove unused libraries and duplicated dependencies.
Optimise interaction patterns so that only the necessary part of the UI updates on each action.

3. CLS – Are Layout Jumps Annoying Your Users?

CLS is about visual stability. It measures how much things move around unexpectedly while the page is loading. We’ve all had that moment: you go to tap a button, the content jumps, and you end up clicking an ad instead. That’s exactly what CLS is designed to capture.

CLS ranges:

Good: ≤ 0.1
Needs improvement: 0.1–0.25
Poor: > 0.25

Common causes of layout shift:

Images or videos without width and height attributes.
Banners and ads injected into the page without reserving space.
Late-loading web fonts that change text size after render.
Elements dynamically added above existing content.

Practical ways to improve CLS:

Always reserve explicit width and height (or aspect ratio) for images and videos.
Reserve fixed slots for ads, banners, and dynamic widgets.
Use font-loading strategies (like font-display: swap) to minimise layout changes.
Avoid inserting new elements above the fold after initial render unless absolutely necessary.

How Do You Measure Core Web Vitals?

To work on Core Web Vitals effectively, you need both lab data (for debugging) and field data (for reality):

PageSpeed Insights: Enter a URL and you’ll see lab scores plus field data from the Chrome User Experience Report if available.
Google Search Console > Core Web Vitals: Shows grouped URL performance across your site and highlights which sets of pages are good, need improvement, or are poor.
Chrome DevTools & Lighthouse: Useful for local testing and pinpointing which resources or scripts are causing delays.
Real User Monitoring (RUM) tools: For larger sites, dedicated RUM tools give ongoing visibility into UX on real devices and networks.

Google typically evaluates Core Web Vitals based on the 75th percentile of real user experiences — in other words, it cares about the experience of most users, not just the best or worst cases.

Core Web Vitals and SEO: What’s the Relationship?

Core Web Vitals alone won’t magically put you at the top of page one. Relevance and overall content quality still come first. But when two pages are similar in relevance and intent, the one with the better user experience — reflected in stronger Core Web Vitals — has a clear advantage.

The best way to think about it: Core Web Vitals act like a multiplier on top of already good content. They help reduce bounce, support better engagement and conversions, and make your page a stronger candidate when Google compares similar results.

Turning Core Web Vitals into a Practical Optimisation Plan

Instead of obsessing over numbers alone, it helps to think in three layers: backend, frontend, and UX/design.

1. Backend and Infrastructure

Choose hosting with fast, consistent response times.
Use a CDN to reduce latency for users in different regions.
Enable compression (Gzip or Brotli) and proper caching headers.
Monitor and improve TTFB — many LCP issues start on the server.

2. Frontend Assets and Code

Optimise and serve responsive images; avoid oversized assets.
Minify and bundle CSS and JS sensibly; remove unused code.
Defer or lazy load non-critical scripts and below-the-fold images.
Keep JavaScript bundles as lean as possible; every kilobyte affects INP.

3. UX and Layout

Ensure the primary content appears quickly and clearly above the fold.
Reserve space in the layout for dynamic elements (ads, pop-ups, widgets).
Use readable typography and clear visual hierarchy across devices.
Avoid flashy but heavy animations that don’t add real value.

A Quick Checklist for Understanding and Improving Core Web Vitals

Have you reviewed the Core Web Vitals report in Search Console to see which URL groups are failing?
Have you tested your key pages in PageSpeed Insights and noted LCP, INP, and CLS values separately?
Are your hero images, fonts, and critical resources prioritised and optimised, or still loaded in a generic, theme-default way?
Have you audited your JavaScript bundle size and identified long tasks that block the main thread?
Do you reserve layout space for ads, banners, and lazy-loaded components, or do they push content down as they appear?
Have you tested the site on a real mobile device over a normal (not perfect) network connection?
Do you revisit and re-measure after each optimisation cycle, or was it a one-time PageSpeed check you did and forgot about?

In the end, Core Web Vitals are not there to distract you from content — they exist to make sure your good content is delivered in a smooth, frustration-free way. When strong content, thoughtful UX, and solid Core Web Vitals come together, users win, your business wins, and your visibility in search is far easier to defend.