A print engine simulator (110) is disclosed. The simulator (110) is adapted for use in a development system including a print controller (100) adapted to communicate with a print engine (106) thereby to control said print engine (106). The simulator comprises interpreter means for interpreting a communication from the print controller (100) into hierarchical communication elements, a state machine representation of the print engine (106), said state machine being responsive to the communication, and display means adapted to display at least one of the communication from the print controller (100), the hierarchical communication elements, and an associated communication from the state machine.