CLS (Cumulative Layout Shift)

Cumulative Layout Shift (CLS) is a Core Web Vitals metric that measures the visual stability of a webpage. It quantifies how much the page layout shifts unexpectedly during loading, which can be frustrating for users. A good CLS score is under 0.1. Between 0.1-0.25 needs improvement, and over 0.25 is considered poor. Layout shifts often occur when images load without specified dimensions, ads appear dynamically, or fonts cause text to reflow. To improve CLS: always specify width and height attributes for images and video elements, reserve space for ads and dynamic content, use fixed sizes for embedded content, and implement font-display: swap for web fonts.