Matan · SEO · Performance

LCP (lab)

Largest Contentful Paint should occur within 2.5s on mobile lab data (PageSpeed Insights).

Pass condition in our engine: Lab LCP (mobile) is under 2.5s when PageSpeed Insights is available.

1. Problem description

LCP is the hero image or largest heading. Slow LCP is the Core Web Vital users feel as “the page finally appeared”. This check calls Google’s lab test for the exact URL — it is not a site-wide crawl. It requires a PageSpeed API key on the server.

2. Most common causes

  • Unoptimised hero bitmap (5MB PNG).
  • Render-blocking fonts and CSS.
  • Slow TTFB so the LCP element is discovered late.

3. How to fix it

  1. Serve a compressed, correctly sized hero (AVIF/WebP) with fetchpriority=high.
  2. Preload the LCP image; inline critical CSS.
  3. Fix TTFB and avoid client-only rendering of the hero.

Test this check

We fetch only this URL (plus robots.txt / llms.txt at the domain root when the check needs them). We do not crawl the rest of the site like a full report.

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