This tool from an ex-Google engineer…

This tool from an ex-Google engineer checks and visualizes the Cumulative Layout Shift of any website.

Cumulative Layout Shift is a “Core Web Vital” metric that measures “the instability of content by summing shift scores across layout shifts that don't occur within 500ms of user input. ”

…or another way to put it:

“Have you ever visited a website and was about to click a link to an article, and then… the layout suddenly moves, an ad appears, and somehow instead of clicking on the article you wanted to read, you click on the useless ad?”