First CPU Idle measures when a page is minimally interactive, or when the window is quiet enough to handle user input. It is a non-standard Google web performance metric. Generally, it occurs when most, but not necessarily all visible UI elements are interactive, and the user interface responds, on average, to most user input within 50ms....First CPU Idle measures when a page is minimally interactive, or...time Help improve MDN Was this page helpful to you? Yes No Learn...