The Dresden OCL Toolkit is all about the Object Constraint Language (OCL). OCL is part of the well-known Unified Modelling Language (UML). It extends the UML's graphical notation with the possiblity of adding more formally defined textual constraints on method invocations and on class structures as a whole. Many aspects of a model that cannot be expressed adequately with the graphical notation alone find their representation in OCL constraints.

So, where does the Dresden OCL Toolset come into play? As its name indicates it is not some standalone solution. Instead, many of these tools are meant to be used as a library, integrated into other tools, but there exist also some standalone tools in the Toolkit.