One embodiment of the invention provides a computer-implemented method for collaborative three-dimensional (3D) markup. In this embodiment, the method includes obtaining a 3D representation of a shape on a client using a web-based interface, displaying the 3D representation of the shape in a user workspace, marking directly on a portion of the 3D representation of the shape in the user workspace, displaying the marked-up 3D representation of the shape, and sending the marked-up 3D representation of the shape to one or more additional clients using the web-based interface, wherein the additional clients are capable of displaying the marked-up 3D representation of the shape in their respective user workspaces.