This paper introduces TAGS (Transducer Automata Graphical Simulator), a software tool for teaching different aspects of transducer automata theory, a theoretical topic which underlies many aspects of the design of sequential digital circuits. TAGS allows to simulate both Moore and Mealy transducer automata, integrating different theoretical concepts associated with them. The student can define an arbitrary transducer automaton in an interactive way, being able to simulate and trace its behavior by means of different views.