Time to interactive

Time to Interactive (TTI) is a non-standardized web performance 'progress' metric defined as the point in time when the last Long Task finished and was followed by 5 seconds of network and main thread inactivity.

TTI, proposed by the Web Incubator Community Group in 2018, is intended to provide a metric that describes when a page or application contains useful content and the main thread is idle and free to respond to user interactions, including having event handlers registered.

Caveat:

TTI is derived by leveraging information from the Long Tasks API. Although available in some performance monitoring tools, TTI is not a part of any official web specification at the time of writing.