What is First Input Delay (FID)?

First Input Delay (FID) is a user-centric metric that measures the time it takes for a web page to respond to a user's first interaction. This includes clicks, taps, or keyboard input from the user.

FID is an important metric because it helps measure how responsive and interactive a website or web application is. A long FID can lead to frustration for users, causing them to abandon the site and seek alternatives.

In order to optimize FID, developers need to ensure that their website's JavaScript code is efficient and does not cause any unnecessary delays in response times.