Regex Nfa

Build and step through a Thompson NFA for a defined regular-expression subset, with epsilon closures shown as active states.

About this tool

Build a Thompson NFA, then Step consumes one input character and highlights its ε-closure. The supported grammar is literals, ., alternation, grouping, *, +, ?, positive character classes and \d, \w, \s. It is not a JavaScript-regex engine: escapes, anchors, negated classes and lookarounds are unsupported.