1. A system comprising: at least one processor of a computing device; a memory of the computing device; and an animation development tool comprising at least one program module loaded into the memory causing the at least one processor to: receive a document closure for a web page of an application, the web page including an animation; generate a data structure representing the animation; preview the animation in the animation development tool without running the application; and convert user gestures manipulating properties of the animation to changes to the data structure.