First Input Delay (FID)

First Input Delay (FID) was historically a Core Web Vitals metric that measured the time from when a user first interacted with a page (e.g., clicking a link or tapping a button) to the time the browser was actually able to begin processing event handlers in response to that interaction. FID specifically quantified the frustration of clicking a button on a seemingly loaded page, only to have the site freeze because the main thread was paralyzed by heavy JavaScript execution. Google has officially replaced FID with Interaction to Next Paint (INP) to provide a more comprehensive measurement of overall page responsiveness.

First Input Delay (FID) Simplified

First Input Delay was Google’s measurement of how long it took for a website to actually respond when you clicked a button. If the website was too busy loading heavy code in the background, the button wouldn’t work immediately, causing Google to lower its ranking.