Courtesan is the Kingly companion of choice for debugging and tracing Kingly state machines. The extension provides a slick UI for monitoring the outputs and internals of a Kingly state machine. It shows you how the events passed through the machine, together with the computed outputs. It also shows you the key steps of the machine computation (transition take, guards evaluation, etc.) and the evolution of the state of the state machine.
Good support for the library