At this point your page has reached FCP . But the question is: can users interact with your page?
Well, that's exactly what FID measures: how long it takes a user to interact with your page .
Examples of interactions are:
Choose an option from a db center.uk menu.
Clicking on a link while browsing the site.
Enter email into a form.
Open an "accordion text" on mobile devices.
Google considers FID important because it takes into account how real users interact with websites .
And, as with FCP, it has specific criteria for defining an acceptable FID.
Google's first input delay guidelines
FID technically measures how long it takes for something to happen on a page .
In that sense, it’s a page speed score, but it goes a step further and measures how long it takes users to actually do something on your page.
For a page that is 100% content (like a blog post or news article), FID is probably not a big deal. The only real "interaction" the user makes is scrolling or pinching to zoom in or out.
In fact, my Search Console doesn't even report the FID value for my site.
Backlinko – GSC – Core Web Vitals
I think it's because I don't have any login pages or other pages where someone has to enter something right away.
But for a login page , a signup page, or other pages where users need to click on something quickly, the FID is very important.
For example, think about the loading experience of a page like this:
On a login page like this, the loading time of the content is not that important: what matters is how quickly you can start typing your login details.
