~/tools/core-web-vitals-checker

Core Web Vitals Checker

Catch the page-level issues that wreck your Core Web Vitals — slow TTFB, lazy-loaded hero images, render-blocking scripts, and layout shift — before they cost you rankings.

§ what this tool checks

Rules applied to every scan.

Core Web Vitals are a confirmed Google ranking factor, but the field scores you see in Search Console are downstream of fixable, page-level mistakes. This tool measures your server's time to first byte and inspects the HTML for the patterns that wreck LCP and CLS — lazy-loaded hero images, render-blocking scripts, and images without dimensions — so you can fix the causes instead of guessing at the symptoms.

Time to First Byte (TTFB) measured live

Above-the-fold (LCP) images that are lazy-loaded

Render-blocking scripts and stylesheets in the <head>

Images missing width/height that cause layout shift (CLS)

Below-the-fold images missing loading="lazy"

Excessive external scripts slowing the page

§ faq

Questions, answered.

What are Core Web Vitals?

Core Web Vitals are three user-experience metrics Google uses as ranking signals: Largest Contentful Paint (LCP) measures loading speed, Cumulative Layout Shift (CLS) measures visual stability, and Interaction to Next Paint (INP) measures responsiveness. Google considers a page "good" when LCP is under 2.5s, CLS is under 0.1, and INP is under 200ms.

Why does this tool show lab signals instead of a field score?

Google's official Core Web Vitals scores come from real-user (field) data collected over 28 days in the Chrome UX Report — they can't be measured in a single request. What this tool does is inspect the page-level causes of poor vitals: a lazy-loaded hero image, render-blocking scripts, missing image dimensions, and a slow TTFB. Fix these and your field scores follow.

How does TTFB relate to Core Web Vitals?

Time to First Byte is how long your server takes to start responding. It is not a Core Web Vital itself, but it is the foundation of LCP — every millisecond of slow server response is a millisecond your largest element cannot start painting. web.dev considers TTFB good at 800ms or under. A slow TTFB caps how fast your LCP can ever be, no matter how optimized the front end is.

What is the most common Core Web Vitals mistake?

Lazy-loading the hero image. Developers add loading="lazy" to every image for performance, but the largest above-the-fold image is almost always the LCP element — deferring it directly delays LCP. The fix is to never lazy-load above-the-fold images and to add fetchpriority="high" to the LCP image instead. Missing width/height attributes (causing layout shift) is a close second.

§ run the full audit

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§ other tools

Check another thing.

Single-purpose inspectors for when you need to verify one thing.

01Meta Tag CheckerCheck your page title, meta description, viewport, charset, and robots tags.02Robots.txt ValidatorValidate your robots.txt file for syntax errors and blocking rules.03AI Crawler CheckerTest if ChatGPT, Claude, and Perplexity can actually read your page — not just whether your robots.txt says they can.04Open Graph Tag PreviewCheck your Open Graph and Twitter Card tags for social media sharing.05Sitemap ValidatorValidate your sitemap.xml file format and URL count.06Heading Structure CheckerAnalyze your H1-H6 heading hierarchy for SEO best practices.07SSL Certificate CheckerCheck your SSL certificate: expiry date, issuer, and trust chain.08Redirect CheckerTrace the full redirect chain for any URL — every 301, 302, and hop.09Structured Data ValidatorValidate your JSON-LD schema markup for missing fields and errors.10Broken Link CheckerScan a page for internal links that return 404s and server errors.11Security Headers CheckerScan your HTTP response headers for CSP, HSTS, and other protections.12Canonical Tag CheckerCheck your canonical tag and confirm it points where it should.