This paper shows the debugging facilities provided by the SLAM system. The SLAM system includes i) a specification language that integrates algebraic specifications and model-based specifications using the object oriented model. Class operations are defined by using rules each of them with logical pre and postconditions but with a functional flavour. ii) A development environment that, among other features, is able to generate readable code in a high level object oriented language. iii) The generated code includes (part of) the pre and postconditions as assertions, that can be automatically checked in the debug mode execution of programs. We focus on this last aspect. The SLAM language is expressive enough to describe many useful properties and these properties are translated into a Prolog program that is linked (via an adequate interface) with the user program. The debugging execution of the program interacts with the Prolog engine which is responsible for checking properties.