re: Measuring Cumulative Layout Shift (CLS) in WebPageTest VIEW POST


I want to check the value for my site miniimagesvideos.com/
I run the site against developers.google.com/speed/pagesp.... Field value is coming as 0.26, while the lab value is coming as 0.0. I have embed the script in my html pages and keep getting the value as 0. Is there any site which can measure accurately


This is a great question and one of the challenges of measuring CLS in the lab.

Field data is inclusive of all of the actions users take on the website like scrolling and interacting with buttons. CLS may be occurring in these kinds of scenarios that lab tools like WebPageTest and Lighthouse don't currently simulate by default. With CLS gaining popularity as a Core Web Vital metric, I'd love to see lab tools incorporate more user-like behaviors to be comparable with field data.

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