Regex Tools

Test, replace, and visualize regular expressions with match highlighting and explanation.

20 tools available, all running locally in your browser.

Regex Complement
Compute the true complement of a regex language — every string it does not fully match — as a ready-to-use ^...$ pattern, via DFA inversion with minimization, in your browser.
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Regex Contains
Regex Contains — pure client-side tool. Privacy-first, no server round-trip.
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Regex Difference
Build a regex for 'strings matching pattern A but not pattern B' from two patterns, one per line. Semantics are asymmetric: A must match from the start of the string, while B is rejected if it occurs anywhere. Output shape: (?=A)(?!.*B).*
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Regex Equivalent
Check whether two regexes match exactly the same strings — semantic equivalence via product-DFA analysis, with a shortest counterexample string when they differ. Input: two patterns on separate lines.
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Regex Escape String
Regex Escape String — pure client-side tool. Privacy-first, no server round-trip.
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Regex Explain
Regex Explain — pure client-side tool. Privacy-first, no server round-trip.
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Regex Extract Groups
Regex Extract Groups — pure client-side tool. Privacy-first, no server round-trip.
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Regex Fuzz
Regex Fuzz — pure client-side tool. Privacy-first, no server round-trip.
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Regex Generate
Generate sample strings that a regex fully matches — distance-guided sampling on its DFA (deterministic for the same pattern, empty language detected), all in your browser.
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Regex Intersect
Build a pattern matching any string that contains both A and B as substrings (lookahead AND). Input: two patterns on separate lines.
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Regex Minimize
Safely minimize a regex — removes only provably lossless constructs (redundant non-capturing groups, empty groups); capture groups are never touched and doubtful cases keep the original.
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Regex Optimize
Regex Optimize — pure client-side tool. Privacy-first, no server round-trip.
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Regex Replace Batch
Regex Replace Batch — pure client-side tool. Privacy-first, no server round-trip.
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Regex Test Batch
Regex Test Batch — pure client-side tool. Privacy-first, no server round-trip.
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Regex to DFA
Convert a regex to a DFA via subset construction — full transition table plus the minimized state count (Moore algorithm), computed entirely in your browser.
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Regex to NFA
Convert a regex to a Thompson NFA with ε-transitions via formal construction — states, symbol and ε edges, start and accept states, computed entirely in your browser.
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Regex Unescape String
Regex Unescape String — pure client-side tool. Privacy-first, no server round-trip.
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Regex Union
Regex Union — pure client-side tool. Privacy-first, no server round-trip.
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Regex Validate Pattern
Regex Validate Pattern — pure client-side tool. Privacy-first, no server round-trip.
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Regex Visualize
Render a regex as a Thompson NFA state diagram in Graphviz DOT format — ε-transitions, branches and quantifier loops visible; paste into any graphviz renderer.
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