First Input Delay

First Input Delay (FID), developed by Google to measure the time from a user first interacts with your website. FID is typically quick and fairly simple to implement. It accurately measures the time from clicking a link, taps on a button, or use a custom, Javascript powered control to the time when the browser can respond to that user interaction.

First Input Delay is an important user-centric metric for measuring load responsiveness. If you want to provide good user experience, then your website should strive to have a First Input Delay of fewer than 100 milliseconds.