First Input Delay (FID) is a user experience metric that makes up one part of the Core Web Metrics.
But how to make sense of this metric? Let’s take a look at FID and consider what it does and its role in Google’s Core Web Metrics.
Rather than just a random metric that is randomly selected by Google, First Input Delay has real-world benefits to brands and retailers that affects traffic, leads, sales, and revenue.
The definition of First Input Delay
First Input Delay is the measurement of time that it takes for a web browser to respond to the first interaction of a visitor of a website while it’s loading.
Such interaction covers a range of things such as clicking on a button, on a link, and a keypress. And it includes those text input areas, the dropdowns, and the checkboxes.
However, scrolling and zooming are actions that don’t count as interactions given that there is no response that is expected from the actual site itself.
The essence of First Input Delay is to measure the responsiveness of a website while it’s loading.
First Input Delay typically occurs when text or images download on a page in a non-orderly way, which causes the page to pause excessively. Then start. And pause again before restarting. This in turn causes unresponsive behavior for a website visitor when they try to interact with the page.
I like to think about First Input Delay as a simile for a traffic jam that is caused when the lights malfunction and flicker and chaos ensues.
According to Google, they describe input latency in the following way: “In general, input delay (a.k.a. input latency) happens because the browser’s main thread is busy doing something else, so it can’t yet respond to the user.
The curse of poor scores related to First Input Delay is the unorganized downloading of images and text. And so the way to fix the problem is to thoroughly organize how these images and texts are presented to the browser.
And this means using HTML to control how scripts are downloaded. It means the optimization of images. And it means comprehensively omitting those texts and scripts that were simply unnecessary. The point is to optimize what is actually downloaded to get rid of the rolling pauses and starts of downloads on a webpage.