A system for extending the functionality of a web-based, three-dimensional modeling in a browser application is stored as instructions on a computer-readable medium. The instructions include an interface module that may receive user commands from the browser application that define a script including functions to modify or create a 3D model. The script instructions may cause a rendering of the 3D model to be displayed in a window controlled by the browser application. A modeling engine as a compiled browser plug-in may extends the functionality of the browser application. Further, the modeling engine may include functions to interpret model data corresponding to a 3D model and render the 3D model in accordance with the script. Further instructions include a script interface layer that may expose the modeling engine functions to the interface module for use by the script functions. The script functions extend the modeling engine functions.