We describe the design of VIP, a graphical front-end to the model checker SPIN. VIP supports a visual formalism, called v-Promela that connects the model checker to modern hierarchical notations for the specification of object-oriented, reactive systems. The formalism is comparable to formalisms such as UML-RT, ROOM, and Statecharts, but is presented here in a framework that allows us to combine the benefits of a visual, hierarchical specification method with the power of LTL model checking provided by SPIN. Like comparable formalisms, VIP can describe hierarchies of behaviour and of system structure. The formalism is designed to be transparent to the SPIN model checker itself, by allowing all central constructs to be translated mechanically into basic PROMELA, as already supported by the existing model checker.