This article presents the stages of software development based on agents used to achieve the main goal of this article, which is the detection of frauds in municipal taxes. In the stages of analysis and design of the system, the methodology MAS- CommonKADS and the ontology ONTOMADEM were used. A generic user model, obtained from historical data from actions of the users, and inference functions of behavior are proposed. The results obtained from tests in Sao Luis municipal government, Maranhao state, in Brazil, are also reported here.