Was ist CLS (Cumulative Layout Shift)?
Kurzdefinition
CLS misst die Gesamtmenge unerwarteter Layout-Verschiebungen während des gesamten Lebenszyklus einer Seite und quantifiziert, wie stark sich sichtbare Inhalte verschieben.
Cumulative Layout Shift (CLS) is a Core Web Vital that measures visual stability. It quantifies how much the content on a page moves around unexpectedly as it loads. A layout shift occurs when a visible element changes its position from one rendered frame to the next without user interaction.
A good CLS score is under 0.1. Between 0.1 and 0.25 needs improvement, and above 0.25 is poor. The score is calculated by multiplying the impact fraction (how much of the viewport was affected) by the distance fraction (how far elements moved).
Common causes of layout shift include images and videos without dimensions (the browser doesn't know how much space to reserve until they load), ads or embeds that load dynamically and push content down, web fonts that cause text to resize when they load (Flash of Unstyled Text), and content that's dynamically injected above existing content.
Fixing CLS typically involves always including width and height attributes on images and videos, reserving space for ads and dynamic content, using font-display: swap or optional for web fonts with preloading, and avoiding inserting content above existing content. CSS properties like aspect-ratio and min-height can also help reserve space.
Warum es wichtig ist
Layout shifts are one of the most frustrating user experiences on the web. You're about to click a link, and suddenly the content jumps because an ad loaded. You're reading an article, and the text shifts because an image rendered. These unexpected movements cause misclicks, lost reading position, and user frustration.
As a Core Web Vital, CLS affects your Google rankings. But beyond SEO, fixing CLS directly reduces user frustration and can prevent costly misclicks, especially on mobile where ad-related layout shifts might cause accidental ad clicks.
Praxisbeispiele
A news website reduced their CLS from 0.42 to 0.05 by reserving space for ad slots and adding dimensions to all images, resulting in 30% longer average reading sessions
An e-commerce product page had a CLS of 0.35 because customer review stars loaded late and pushed the "Add to Cart" button down, causing misclicks; fixing this improved the add-to-cart rate by 8%
A blog fixed their CLS issue caused by web fonts loading late by preloading the font file and using font-display: optional, eliminating text layout shifts entirely
A landing page reserved fixed dimensions for a video embed that was causing content below it to jump, bringing CLS from 0.28 to 0.02
Verwandte Begriffe
Core Web Vitals
Core Web Vitals sind drei spezifische Metriken von Google, die die reale Nutzererfahrung auf Websites messen: Ladeleistung (LCP), Interaktivität (INP) und visuelle Stabilität (CLS).
LCP (Largest Contentful Paint)
LCP misst die Zeit, bis das größte sichtbare Inhaltselement einer Seite — wie ein Hero-Bild oder eine Überschrift — vollständig gerendert ist.
Lazy Loading
Lazy Loading ist eine Technik, die das Laden nicht kritischer Ressourcen wie Bilder unterhalb des sichtbaren Bereichs verzögert, bis sie tatsächlich benötigt werden.
Responsive Design
Responsives Design ist ein Webentwicklungsansatz, der es Websites ermöglicht, sich an alle Bildschirmgrößen anzupassen und korrekt darzustellen.
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