Frameworks and libraries that use annotations are becoming popular. However, there is not enough software engineering support for annotation development. In particular, the validation of constraints in the use of annotations requires further support. In this paper we postulate that annotation frameworks are a projection of the domain model into a programming language model. Using this idea, we have developed a tool that allows the annotation programmer to specify, and then validate the constraints of the annotation framework regarding a given annotated application using a domain model. To validate our approach to the validation of constraints using models, we apply it to the Fraclet annotation framework and compare it to the previous implementation.