Building and Tracing an Automaton Visually
Designing a finite automaton by hand on paper and then manually tracing whether it accepts a given string is exactly the exercise most automata theory coursework builds around — and it's genuinely error-prone to trace multiple simultaneous NFA states or long input strings entirely in your head, especially once branching (multiple transitions on the same symbol) enters the picture.
An interactive canvas for placing states, drawing labeled transitions, and marking start/accept states removes the tedium of redrawing a diagram for every small design change, while step-by-step trace execution shows exactly which state (or, for an NFA, which set of states) the automaton occupies after each input symbol — making it immediately visible whether and why a given string is accepted or rejected, rather than just getting a final yes/no answer.
This kind of direct manipulation and tracing is especially valuable for NFAs specifically, since the "being in multiple states at once" behavior that makes NFAs flexible to design is also exactly the part that's hardest to reason about without a visual aid tracking every active state in parallel.