At Google I/O ‘22, Annie Sullivan and Michal Mocny introduced a new metric named Interaction to Next Paint, or INP.
The news came almost a year after Google first announced that they were working on a new and better responsiveness metric.
As it turns out, there is a chance that INP will be added to Core Web Vitals and eventually can replace First Input Delay (FID). But nothing is confirmed yet.
Here’s what Michal Mocny had to say about that:
While it’s still experimental, you can already measure your site’s INP. But before that, you have to know how the metric works.
Interaction to Next Paint (INP) is an experimental field responsiveness metric that records the latency of all interactions throughout the entire page lifecycle. Then, the longest delay from all interactions is recorded as the page’s INP.
The difference between Interaction to Next Paint and First Input Delay (FID) comes from the fact that the new metric measures all interactions, whereas FID only accounts for the first one.
In simple terms, a good FID means that your website has made a good first impression. But INP is more than about first impressions. It covers the entire period from the time the page begins loading to the time the user leaves the page.
Similar to Cumulative Layout Shift, INP is calculated when the user leaves the page, measuring the page’s overall responsiveness through its entire lifecycle.
The interactions that play a part in INP’s calculations are:
Actions like scrolling or mouse movements are not considered interactions.
Each interaction consists of multiple events. An interaction's latency consists of the single longest duration of any event that is part of the interaction. The duration is the sum of the following periods:
To provide “good” responsiveness to your users, you should strive to have an INP of 200 milliseconds or less.
An INP between 200 and 500 milliseconds means your page’s responsiveness needs improvement.
And if you have an INP of 500 milliseconds or above, it means that your visitors are experiencing poor responsiveness.
To ensure you're hitting this target for most of your users, a good threshold to measure is the 75th percentile of page loads, segmented across mobile and desktop devices.
There are several ways to measure your site’s INP:
The fact that a page is loaded doesn’t mean that the user interacted with it. This can occur for several reasons:
In these cases, no INP value will be reported.
“Interaction to Next Paint is a huge step toward a better way to measure the user experience on the web. Undoubtedly, it’s more comprehensive than First Input Delay, which, as Google says, has its limitations. Nevertheless, INP is still in its early stages of development, and there is a lot more to unfold regarding its usage and effectiveness.” - Ivaylo Hristov, CTO of NitroPack.
Niko is one of the NitroPack storytellers. He is passionate about writing quality content and turning complex optimization concepts into engaging articles.