diagnostic · one of 29free, no counter
Shifts
What moved while the page was loading?
Cumulative Layout Shift is reported as a number by every performance tool and attributed by almost none of them. This watches the document for elements that change position after paint and tells you which ones, by how much, and what pushed them.
Reach itPress ⌘+K on any tab and type shifts.Ctrl+Kon Windows and Linux
TWO BUILDS9 browsers
Chromelisting in reviewFirefoxlisting in reviewBravelisting in reviewOperalisting in reviewEdgelisting in review4 moreChromium browsers: Arc, Vivaldi, Chromium, Opera GXthe Chrome buildin the panel · free, no counter
What this actually is
what moved after first paint and how farAfter a performance report gives you a CLS figure and no address for it. Reload with the panel open - a shift that already happened before you looked cannot be attributed by anything.
Asked about this diagnostic
4 of themWhy is my number different from PageSpeed’s?
Because that one is a field measurement across many real loads on many connections, and this is the load in front of you. They answer different questions: theirs says how bad it is for visitors, this one says which element to change.
It reports a shift I cannot see.
Most of them are invisible at desktop speed and obvious on a cold cache over a slow link. The row names what arrived late, which is the part you can act on whether or not you saw it happen.
Does a shift caused by my own click count?
No. Anything within half a second of an interaction is excluded, exactly as the metric defines it - expanding an accordion is not a layout shift, it is the page doing what it was asked.
Will setting width and height on images fix it?
It fixes the common case, and the reading tells you whether yours is that case. A shift attributed to a font swap or an injected element will not move at all when you add dimensions.
TWO BUILDS9 browsers
Chromelisting in reviewFirefoxlisting in reviewBravelisting in reviewOperalisting in reviewEdgelisting in review4 moreChromium browsers: Arc, Vivaldi, Chromium, Opera GXthe Chrome build63 of these · no host permissions · three free audits