Fast prototyping is a quick and cost effective de velopment of a (minimum) viable version of a software useful to some purpose (e.g., requirements verification or design val idation), which can be discarded or refactored to become the version of the software to be delivered. In this paper we propose a model-driven approach for the fast prototyping of Rich Internet Applications (RIAs). Starting from the conceptual model of a RIA, intermediate models and the source code of a ready-to deploy application prototype are automatically generated through a model-driven development process which exploits well known model-driven engineering frameworks and technologies including Eclipse EMF, GMF, and Xpand. Compared to traditional, non model-driven, prototyping approaches, our proposal allows to drastically reduce the overall prototyping effort to just the effort required to define the conceptual model of the application, as the rest of the process is substantially automatic. The paper describes the overall RIA prototyping approach, the supporting tools and adopted technologies, along with the results from a case study carried out for validation and verification purposes.