Finite state machines are provided to run instances of user-defined routines within a computing system. The finite state machines and updates to the finite state machines are user-defined and are checked for compliance with one or more prescribed schemas by a finite state machine engine. Compliant finite state machine specifications are interpreted for the plurality of states and transitions that constitute the finite state machine. Requested instances of a finite state machine specification are initiated by the finite state machine engine, which creates proxies to monitor the current state of any given requested instance.