A method, system, and computer-readable medium is described for creating a prototype GUI for conversion into an actual GUI whose appearance when displayed matches the appearance of the prototype GUI. In some situations, multiple personnel may participate in the process, such as a non-technical GUI designer that specifies the prototype GUI appearance information and a technical GUI developer that specifies various non-appearance information for a corresponding actual GUI. A prototype GUI is first created based on layout and other appearance information specified for various GUI elements, and corresponding proxy GUI objects are generated that store appearance information but not various non-appearance information used as part of an actual GUI. Proxy GUI objects for a prototype GUI can then be converted into actual GUI objects for use with an actual GUI, and various non-appearance information can be specified for the actual GUI objects in various ways.