First Input Delay (FID).
An important component to measure user experience is First Input Delay. FID is the delay between when the user clicks on something and the time the page responds to and starts processing that action. This can be a click on a link or a button on a page. FID interactions are discrete and finite; scrolling and zooming on a page cannot be properly measured through FID.
The Google metric only measures the first interaction in milliseconds (ms). If the user becomes frustrated during the first visit, chances are they will not return quickly. Despite only measuring the initial input, it is important that other input components on a page are also optimized.
A good FID
The two main components of FID are:
- Speed - If the FID is under 100 milliseconds (ms), your page is in tip-top shape. According to Jacob Nielsen and Google, 0.1 seconds is the limit to make the user feel that a system is instantly responsive.
- Interactivity - Can be measured with the Time To Interactive (TTI) performance statistic. Think of this as seeing the product fly to the basket when you click on it. Otherwise, a user may click on the shopping cart 10 times in the meantime, after which it appears that the product ended up in the basket 10 times. This makes for a poor user experience
Core Web Vitals and FID
First Input Delay is one of Google's three Core Web Vitals that measure a page's page experience. FID measures whether your Web site's interface feels smooth. The user's feeling is most important here. If a user clicks on something and there is no form of confirmation that something is actually happening, it may feel like the page is crashing or unresponsive. Google's Core Web Vitals on pages consist of:
