Regex to Automaton
Under the hood a regular expression is a finite automaton — a little machine with states and arrows. This visualizer takes classic regexes over the alphabet {a, b}, builds the automaton, and lets you feed it strings: the active states light up as each character is consumed, ending green if the string is accepted and red if not. Watching several states glow at once makes nondeterminism — the N in NFA — suddenly concrete.
Runs 100% in your browser — simulations are computed locally on your device.
Read the full guide to this tool
Notes
- Thompson’s construction turns any regex into an NFA with at most 2 states per regex symbol.
- An NFA can be in several states at once; the subset construction turns it into a DFA.
- Regular expressions, NFAs and DFAs all describe exactly the same languages — the regular languages.
- Runs 100% in your browser — simulations are computed locally on your device.
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