Cumulative Layout Shift
Cumulative Layout Shift (CLS) is a Core Web Vitals metric that measures unexpected layout shifts during page load. It evaluates how stable content is displayed during the initial Rendering . A good CLS score below 0.1 is critical for user satisfaction and directly influences the PageSpeed rating by Google.
Why is CLS relevant?
Unexpected layout shifts significantly impair the user experience. When content suddenly moves, incorrect clicks can occur or the reading flow is interrupted. A good CLS score contributes substantially to a stable perception of the page and complements metrics like Largest Contentful Paint and First Contentful Paint .
Typical causes of layout shifts
CLS frequently occurs due to missing size attributes for images or embedded content, dynamically loaded elements, or late-loading fonts. Unoptimized stylesheets without targeted prioritization – for example, without Critical CSS – can also cause visual instability.
Technical optimization
To reduce CLS, fixed layout containers should be defined, media should be given fixed dimensions, and asynchronous content should be loaded in a controlled manner. In combination with Caching and structured Lazy Loading , visual stability can be significantly improved.
How we use it
At BTECH Solutions, we eliminate CLS sources already in component design: all images receive fixed width/height attributes, fonts are loaded with font-display:swap and fallbacks, and Lazy Loading areas use placeholders with fixed dimensions. On btech-solutions.eu, we achieve a CLS of 0.00 – measured in Chrome Field Data. Our Responsive Design approach accounts for layout stability across all breakpoints from the start.