Cumulative Layout Shift (CLS)
Cumulative Layout Shift (CLS) is one of Google's Core Web Vitals that measures visual stability. It quantifies unexpected layout shifts of visible page elements. A high CLS score indicates that page elements are moving around unexpectedly, which is frustrating for users and a sign of poor frontend performance. CLS is calculated by tracking the sum of all individual layout shift scores that occur without user input during the entire lifespan of the page.
Related web performance terms
- CDN (Content Delivery Network)
A CDN, or Content Delivery Network, is a globally distributed network of servers designed to deliver web content to users quickly and efficiently.
- CORS (Cross-Origin Resource Sharing)
CORS is a browser security feature that uses HTTP headers to manage whether a web page from one domain is allowed to fetch resources from another domain.
- CPU time
CPU time is the amount of time the Central Processing Unit (CPU) of a user's device spends processing the scripts and rendering a webpage.
- Cache
A cache is a high-speed, temporary storage layer designed to store copies of website files (like HTML, images, and scripts) closer to the user.