“Core web vitals” is a set of core webpage functionalities that impact user experience. Google’s ranking algorithm update called page experience, which Google rolled out from June to August 2021, incorporates core web vitals as NEW ranking factors for SEO.
The current set of core web vitals includes:
Largest Contentful Paint (LCP)
First Input Delay (FID)
Cumulative Layout Shift (CLS)
In this article, part of our series covering the page cork bicycle zone experience update, I’ll discuss first input delay, or FID:
What is FID?
How can I measure FID?
How does FID impact SEO?
How do I improve my FID score?
What Is First Input Delay (FID)?
FID measures the responsiveness of a page to user events. While technically this could happen throughout the lifespan of a user session on a webpage, in practice, most interactivity problems occur during initial page load. That is because this is when most resources are being downloaded, parsed, executed and rendered.
Google discusses FID here:
First Input Delay (FID) is an important, user-centric metric for measuring load responsiveness because it quantifies the experience users feel when trying to interact with unresponsive pages—a low FID helps ensure that the page is usable. …
Google cites two important reasons why the first input delay is important:
The first input delay will be the user’s first impression of your site’s responsiveness, and first impressions are critical in shaping our overall impression of a site’s quality and reliability.
The biggest interactivity issues we see on the web today occur during page load. Therefore, we believe initially focusing on improving site’s first user interaction will have the greatest impact on improving the overall interactivity of the web.
Keep in mind that FID will not apply to every situation, as Google points out here:
Not all users will interact with your site every time they visit. And not all interactions are relevant to FID … How you track, report on, and analyze FID will probably be quite a bit different from other metrics you may be used to.