A totally unrelated comment; but — there is an animation on that page that moves practically everything on the page about 20 pixels down over the course of 1 second.
I thought that would completely trash the Cumulative Layout Shift core web vital. Because, hey! the layout is shifting in front of my very eyes. But no, the CLS on the page is 0.
Is CLS a misleading metric then?
It's happening as a result of a deliberate animation. The CLS metric relates to initial render. So yes, there is layout shift, but it's not CLS per se.
> The CLS metric relates to initial render.
The CLS measures the total sum of layout shifts over the entire lifespan of a page, not just during initial render.
The layout isn't shifting, so it's not a layout shift.
And it's not unexpected, because it comes from a css transition.
Sure.
It's just that the spirit of Google's core web vitals has been to measure the properties of a web page that have the most impact on users. How quickly content appears on a page, how visually stable the content is, and how long it takes the page to respond to an interaction.
In the case of this page, I don't think it can be considered visually stable at all in the first second after it's loaded.
And yet, core web vitals cannot demonstrate this.