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SEO

What is CLS (Cumulative Layout Shift)?

The total score for unexpected layout shifts while the page loads. Good: <0.1.

Detailed definition

If the layout shifts just as a user is about to press a button and they hit the wrong one, the CLS score goes up. The main causes of a higher CLS: images without a width/height attribute, ads or banners that load late above the fold, and text shifting while web fonts load (FOUT/FOIT). Fixes: size attributes on img/iframe elements, reserved space for ad slots, font-display: optional.

Examples

  • If a product list is lazy loaded without image dimensions being specified, CLS deteriorates.

Related terms

Core Web Vitals The three main metrics Google uses to measure site performance: LCP, INP and CLS. LCP (Largest Contentful Paint) How long the page's main content block (usually the hero image or heading) takes to load. Good: <2.5s, poor: >4s. Schema.org / Structured Data The standard for adding machine-readable data to web pages. Critical for Google rich results and for AI engines. On-Page SEO The SEO optimisation carried out on the page itself: title, meta description, heading hierarchy and content quality. Backlink A link given to your site from another site. One of the most important off-page signals in SEO.
From the same category

Other terms in the SEO category

Schema.org / Structured Data The standard for adding machine-readable data to web pages. Critical for Google rich results and for AI engines. On-Page SEO The SEO optimisation carried out on the page itself: title, meta description, heading hierarchy and content quality. Backlink A link given to your site from another site. One of the most important off-page signals in SEO. Canonical URL The <link rel="canonical"> tag that tells Google the "main" URL of a page. hreflang The link attribute that states which language sits at which URL on multilingual or multi-region sites. Meta Description The short description that appears under the title in Google search results. It directly affects CTR.
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