Cumulative Layout Shift

Definitions

1. A Core Web Vital metric that measures visual stability — how much the page layout unexpectedly shifts during loading. Caused by images without dimensions, dynamically injected content, web fonts causing FOUT, and ads resizing. Score above 0.1 is poor. Fixed by setting explicit dimensions, using font-display: swap, and reserving space for dynamic content.

   In plain English: A measure of how much the page content jumps around as it loads — lower is better.

   Example: "The CLS score is 0.35 because the hero image loads without width/height attributes — the page jumps when it renders. Add dimensions to fix it."

Related Terms

• A/B Testing
• Accessibility
• Pagination
• Skeleton Screen
• First Contentful Paint
• Largest Contentful Paint
• Progressive Loading
• Web Vitals