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What are Core Web Vitals

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Key idea:

Core Web Vitals are three user-facing metrics Google uses to measure UX and factor into ranking: LCP (Largest Contentful Paint — when the main content paints), INP (Interaction to Next Paint — interaction latency, replaced FID in March 2024) and CLS (Cumulative Layout Shift — visual instability). Thresholds: LCP ≤ 2.5s, INP ≤ 200ms, CLS ≤ 0.1.

Below: details, example, related terms, FAQ.

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Details

  • LCP (Largest Contentful Paint): time to largest visible element. ≤ 2.5s = good
  • INP (Interaction to Next Paint): long tail of click latency (replaced FID March 2024). ≤ 200ms
  • CLS (Cumulative Layout Shift): total layout shift without user interaction. ≤ 0.1
  • Measured via Chrome UX Report (CrUX) — real-user data over 28 days
  • Pass threshold = 75th percentile across ≥ 28 days

Example

LCP: 1.8s ✅  |  INP: 180ms ✅  |  CLS: 0.04 ✅

Related Terms

Related guides

PerformanceOverall speed score 0-100
Core Web VitalsLCP, FID, CLS — Google metrics
Page SizeSize of HTML, CSS, JS, images
RecommendationsSpecific tips for improvement

Why teams trust us

Lighthouse
analysis engine
CWV
Core Web Vitals
4
Lighthouse categories
Precise
recommendations

How it works

1

Enter page URL

2

Lighthouse analyzes

3

Get CWV scores & tips

Why Does Site Speed Matter?

Page load speed directly impacts conversion, SEO rankings, and user satisfaction. Google uses Core Web Vitals as a ranking factor. Every extra second of load time cancost up to 7% in conversions.

Lighthouse Analysis

Google Lighthouse-based analysis: Performance, Accessibility, Best Practices, SEO.

Core Web Vitals

LCP (rendering), FID (interactivity), CLS (visual stability) — key Google metrics.

Resource Analysis

Breakdown by type: HTML, CSS, JavaScript, images, fonts. Size, request count, blocking resources.

Actionable Advice

Specific recommendations with savings estimates: image compression, caching, minification, etc.

Mobile vs Desktop

Mobile
  • Tested on Moto G Power emulation (slow CPU)
  • Network: 4G (1.6 Mbps, 150ms RTT)
  • Stricter speed scoring
  • Google indexes mobile-first
  • Priority for SEO optimization
Desktop
  • High CPU performance
  • Fast connection without throttling
  • Scores typically 20-40 points higher
  • Important for B2B and corporate sites
  • Use for baseline comparisons

Who uses this

SEO

Core Web Vitals for rankings

Developers

performance optimization

Marketers

speed = conversions

DevOps

performance regression

Common Mistakes

❌
Unoptimized imagesImages can be up to 70% of page weight. Use WebP/AVIF and lazy loading.
❌
Render-blocking JS in <head>Scripts without async/defer block rendering. Move to end or add attribute.
❌
No static asset cachingWithout Cache-Control, the browser reloads CSS/JS on every visit.
❌
Too many HTTP requestsEach request adds latency. Bundle files, use sprites, or inline critical CSS.
❌
Missing compression (gzip/brotli)Compression reduces text resource size by 60-80%. Enable brotli on the server.

Best Practices

✓
Optimize imagesWebP for photos, SVG for icons. loading="lazy" for images below the fold.
✓
Enable brotli compressionBrotli is 15-20% more efficient than gzip. Configure in nginx: brotli on;
✓
Set up cachingStatic: Cache-Control: max-age=31536000, immutable. HTML: max-age=0, s-maxage=60.
✓
Preload critical resources<link rel="preload"> for fonts and CSS. Reduces LCP by 200-500ms.
✓
Test regularlySpeed degrades over time. Check after each deploy and monthly.

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How-to

Glossary

Research

Alternatives

Frequently Asked Questions

When did INP replace FID?

March 12, 2024. FID (First Input Delay) measured only the first click. INP captures all interactions — better reflects real UX.

Do CWV affect ranking?

Yes. Google confirmed CWV as a signal since 2021. Impact ~5-10% all else equal.

How do I check CWV for my site?

PageSpeed Insights (Google) or <a href="/en/speed">Enterno Speed</a> — both use CrUX field data.

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