RAIL, an acronym for Response, Animation, Idle and Load, is a performance model originated by the Google Chrome team in 2015, focused on user experience and performance within the browser. The performance mantra of RAIL is "Focus on the user; the end goal isn't to make your site perform fast on any specific device, it's to make users happy." There are 4 stages of interaction: page load, idle, response to input, and scrolling and animation. In acronym order, the main tenets are:
- Respond to users immediately, acknowledging any user input in 100ms or less.
- In animating, render each frame in under 16ms, aiming for consistency and avoiding jank.
- Deliver interactive content in under 1 second.