In this paper, we present a tool for automatic prototype generation and analysis (AutoPA2.0) that implements the transformations from UML system requirements models to executable prototypes with the function of checking multiplicity invariants. A UML system requirements model consists of a use-case model and a conceptual class model. Generally, a use case is either described as a system operation which can be defined as a pair of pre and post conditions in the context of the conceptual class model, or described as a sequence of such system operations. AutoPA2.0 can transform the descriptions of use cases into an executable prototype in Java. The execution of each use case is a sequence of basic atomic actions which first check the pre-condition and then enforce the post-condition of the corresponding use case. It helps to improve the understanding between customers and designers. A simple library system is used to explain the method, and illustrate the feasibility of tool as well as its development. © 2008 Elsevier B.V. All rights reserved.