In this paper we review KEE* and ART,† two expert system toolkits. We study their specific competences with respect to existing expert system technologies. Beyond the KEE and ART case study, we show the advantages of evaluating knowledge engineering tools with respect to the classification of the expert system technologies we discuss. Basically, these technologies differ from one another in their underlying problem-solving philosophies. This leads to three different expert system paradigms with specific competences and tools.