1. A method comprising: defining, in a widget editor, a placeholder widget comprising a roughly drawn sketch, the placeholder widget having a text property; defining, in a GUI editor, a prototype graphical user interface (GUI) comprising an instance of the placeholder widget; presenting the prototype GUI to a user, an appearance of the instance of the placeholder widget based on the text property of the placeholder widget; in response to a user selection of the instance of the placeholder widget, presenting a list of second widgets to the user and receiving a user selection of one of the second widgets; in response to the selection of the selected second widget, replacing the instance of the placeholder widget in the prototype GUI with an instance of the selected second widget and transferring the text property of the placeholder widget to the instance of the selected second widget; and updating the presentation of the prototype GUI using the instance of the selected second widget wherein the widget editor is separate from the GUI editor.