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SEOPerformanceCore Web Vitals

Core Web Vitals Explained (and How to Test Yours for Free)

By Gearboxly7 min read

Google has made page experience part of how it ranks pages, and the headline metrics are the Core Web Vitals. They sound technical, but each one measures something a real visitor feels: how fast the page shows up, how quickly it responds, and whether things jump around while it loads.

Here's what each Vital means in plain English, the numbers you're aiming for, and how to measure and improve them without paying for anything.

The three Core Web Vitals

Largest Contentful Paint (LCP) — how long until the biggest thing on screen (usually the hero image or headline) has loaded. It's your 'is this page fast?' metric. Aim for under 2.5 seconds.

Interaction to Next Paint (INP) — how quickly the page responds when someone taps or clicks. A laggy button feels broken even on a 'fast' page. Aim for under 200 milliseconds.

Cumulative Layout Shift (CLS) — how much the page jumps around as it loads. You've felt this: you go to tap a link and an ad pushes it down. Aim for under 0.1.

How to measure yours

Run your page through the free Page Speed Test. It reports all three Vitals — from real Chrome users where available, plus a lab test — for both mobile and desktop, and lists the specific fixes that will help most.

Page Speed TestMeasure Core Web Vitals and Lighthouse scores.

Test mobile first. Most traffic is mobile, Google indexes mobile-first, and phones are where slow sites hurt most.

How to improve LCP (loading)

  • Compress your hero and above-the-fold images — they're the usual culprit. Use the Image Compressor.
  • Serve modern formats like WebP; convert with the Image Converter.
  • Enable gzip or Brotli compression and good caching — check what your server sends with the HTTP Header Checker.
  • Remove render-blocking scripts and unused CSS so content paints sooner.

How to improve CLS (visual stability)

  • Set width and height on every image so the browser reserves space. Find images missing dimensions with the Image SEO Checker.
  • Reserve space for ads and embeds instead of letting them push content down.
  • Avoid inserting content above what the user is already reading.

How to improve INP (responsiveness)

  • Break up long JavaScript tasks so the main thread isn't blocked when someone interacts.
  • Defer or lazy-load non-critical scripts.
  • Keep third-party scripts (chat widgets, trackers) to a minimum — each one competes for the main thread.

After each change, re-test with the Page Speed Test and watch the trend. Small, measured improvements add up.

Tools mentioned in this post

Page Speed TestMeasure Core Web Vitals and Lighthouse scores.Image CompressorShrink JPG, PNG and WebP without uploading.Image SEO CheckerFind images missing alt text and dimensions.HTTP Header CheckerInspect security, caching & SEO response headers.

Frequently asked questions

LCP under 2.5s, INP under 200ms, and CLS under 0.1. Hitting all three on mobile is the goal.

Yes. They're part of Google's page-experience signals. They won't outrank great content, but among similar pages they can tip the balance.

Lab data is a single controlled test; field data reflects what real Chrome users experienced over the last 28 days. Prefer field data when it's available.

Field data only appears for sites with enough real-user traffic. Lower-traffic sites still get full lab metrics.

After any significant change, and periodically — performance regresses over time as pages accumulate scripts and images.

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