WFSC -- a new weighted finite state compiler. This article presents a new tool, WFSC, for creating, manipulating, and applying weighted finite state automata. It inherits some powerful features from Xerox’s non-weighted XFST tool and represents a continuation of Xerox’s work in the field of finite state automata over two decades. The design is generic: algorithms work on abstract components of automata and on a generic abstract semiring, and are independent of their concrete realizations. Applications can access WFSC’s functions through an API or create automata through an end-user interface, either from an enumeration of their states and transitions or from rational expressions.