This paper describes an environment specifically tailored for the design and the rapid prototyping of Web applications. The environment, named WARP (Web Application Rapid Prototyping), offers a set of online software tools, which assist the designer and the user browsing of a Web application, in all its different aspects.The environment is based upon models and techniques already used in the hypermedia, information systems, and software engineering fields, adapted and blended in an original mix. The foundation of the proposal is the conceptual design of Web applications, starting from HDM, a notation for the specification of structure navigation, and presentation semantics.Compared to existing tools, WARP is an aid for analysis and design of Web Application because it introduces a new approach completely on-line (both the design and the execution environment). So the author can immediately formulate and evaluate requirements, specification and designs.A real-life experience of the use of the methodology and of the WARP in academic context are reported.