GRASPER: Constraint Reasoning with graphs. In this paper we present GRASPER, a graph constraint solver based on set constraints. GRASPER is a constraint logic-based reasoning framework aiming to provide a powerful, efficient and intuitive framework for modelling and solving hard combinatorial problems by introducing graph variables. We specify GRASPER’s core and higher level constraints and make use of it to model a problem in the context of biochemical networks showing promising results, when compared to an existing similar solver, for different search heuristics