In this paper a reverse engineering approach for reconstructing UML diagrams at business level of the application domain of a Web Application is presented. In particular the approach allows the reconstruction of the UML class diagram providing an object-oriented conceptual model of the application domain, sequence diagrams modeling the interactions among the identified business objects and use case diagrams modeling the user functionalities provided by the Web Application. Heuristic criteria exploiting source code analysis are used for recovering the diagrams. Tools for implementing these criteria have been produced, and experiments for validating them have been carried out with the support of case studies. Experimental results showed the feasibility and the effectiveness of the proposed approach.