A software modeling method provides concrete modeling guidelines. Use of the guidelines helps designers build rigorous software in a systematic manner. However, the observation of modeling guidelines heavily relies on individual developer. This paper presents a rule syntax and its tool support for describing and verifying the modeling guidelines of UML-based modeling methods. The rule syntax enables one to specify informative messages in a conditional structure that help understand violations of modeling guidelines. We also present tool support that implements the rule syntax to validate modeling guidelines for UML models. We use COMET, a design method for concurrent systems, to demonstrate the approach. We validate the guidelines of COMET for UML models of a robot navigation system and a robot patrol system.