1. A system for routing nets in a circuit, the system comprising: a processor to execute instructions; and instructions stored in a storage device that when executed by the processor perform operations including reading constraint definitions of a plurality of constraints to which the nets of the circuit are to comply; generating at least one constraint handler in response to the constraint definitions, the at least one constraint handler to invoke a routing action associated with a routing engine to route a net; and performing the routing action to improve compliance of the net with the plurality of constraints.