Measure Performance with the RAIL Model

RAIL is a user-centric performance model that breaks down the user’s experience into key actions. RAIL’s goals and guidelines aim to help developers and designers ensure a good user experience for each of these actions. By laying out a structure for thinking about performance, RAIL enables designers and developers to reliably target the work that has the highest impact on user experience.

Every web app has four distinct aspects to its life cycle, and performance fits into them in different ways:

The 4 parts of the RAIL performance model: Response, Animation, Idle, and Load.


RAIL is a lens for looking at a website’s user experience as a journey composed of distinct interactions. Understand how users perceive your site in order to set performance goals with the greatest impact on user experience.

  • Focus on the user.
  • Respond to user input in under 100ms.
  • Produce a frame in under 10ms when animating or scrolling.
  • Maximize main thread idle time.
  • Load interactive content in under 5000ms.