In this paper, a software tool to deal with diagnosis of discrete event systems (DESs) is presented. This tool called On-the-Fly PEtri-Net-based Diagnosability Analyzer (OF-PENDA) implements the techniques developed in [13] for the diagnosis of DESs modeled by labeled Petri nets (LPNs). This technique aims to cope with the state explosion problem which is a major issue when dealing with diagnosis of DESs. In particular, OF-PENDA implements an incremental and on-the-fly algorithm which makes it possible to analyze (K-)diagnosability without necessarily generating the whole state space of the model. Three aspects for OF-PENDA are discussed in this paper: an overview on the implemented technique is given; some features of the tool are discussed; then two illustrative case studies are processed to show the efficiency in terms of time and memory compared with some existing approaches.