First Input Delay [FID]

First Input Delay
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First Input Delay (FID) is measured in milliseconds (ms). It is the time from when a user first engages with a web page (e.g. clicking on a link, tapping a button or another JavaScript-based action etc.). to when the browser responds to that action. It is a measurement taken from when the user first clicks an element.

To put it more simply, First Input Delay helps you ensure that the loading of any critical resources doesn’t make your website feel cumbersome and unresponsive.

The data collected for FID by PageSpeed Insights can vary dramatically depending on various factors, such as varying network conditions and the technical capabilities of devices. A poor FID is often caused by images or scripts that download in a disordered manner, resulting in the page download pausing and restarting multiple times.

As of 12th March 2024, First Input Delay was officially been replaced by Interaction to Next Paint (INP) and is now deprecated from Core Web Vitals performance reports.

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