What is Jank?

Modern browsers try to refresh the content on screen in sync with a device's refresh rate. For most devices today, the screen will refresh 60 times a second, or 60Hz. If there is some motion on screen (such as scrolling, transitions, or animations) a browser should create 60 frames per second to match the refresh rate.

Jank is any stuttering, juddering or just plain halting that users see when a site or app isn't keeping up with the refresh rate. Jank is the result of frames taking too long for a browser to make, and it negatively impacts your users and how they experience your site or app.