Electronic multimedia publishing is increasingly becoming a major industrial activity, and the design of web applications and hypermedia applications in general needs to become a well-organized and efficient process. The most important factor in making web design efficient and effective is the availability of a suitable design model. Considering that no model can be exploited to its maximum potential unless it is supported by a proper set of development tools, in this paper we present an execution environment called the JWeb II navigation engine, which is a part of a suite of tools called JWebII. JWeb II is based on the HDM model and supports all the different phases of web prototyping development.