Time to Interactive (TTI)

Time to Interactive is a performance metric that measures the time it takes for a page to become fully and reliably responsive to user input. It marks the point where the page has displayed useful content (FCP) and the Main Thread is free of any Long Tasks that would prevent it from responding to an interaction quickly. While it was a key lab metric for many years, INP has now superseded it as the official Core Web Vital for measuring interactivity.