Generate random strings that match any regex
Paste a pattern and produce ten synthesized strings, each verified against the original regex. Refresh for a fresh batch. Runs locally.
ZZZ-1111VVV-7777GGG-0000ZZZ-3333OOO-2222YYY-5555LLL-5555NNN-2222LLL-1111EEE-5555How to generate strings from a regex
Drop in any regex and produce random strings that satisfy it — useful for fixtures, fuzz inputs, and demos.
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Paste pattern
Any JavaScript regex works. Character classes, quantifiers, escapes are all understood.
Patterns compile through the JavaScript RegExp constructor, so syntax errors surface immediately and engine quirks like Unicode property escapes (\p{L}) work when the u flag is on.
patternECMAScriptliteralliveinput · literalregex · regex[A-Z]{3}-\d{4}loaded · ECMAScriptPCRE · ready - 02
Read 10 samples
Each row shows a freshly generated string plus a ✓/✗ verifying it matches.
Each flag character mirrors the ECMAScript literal: g enables iteration, i folds case, m anchors per line, s lets . match newlines, u unlocks proper Unicode, y is sticky, and d emits indices.
flagsoptionsg · i · mliveconfig · optionssamples · flagsMZX-4291 RTQ-0083flags applied · liveECMA · live - 03
Refresh and copy
Click Refresh for a new batch. Copy grabs all ten ready for fixtures.
Watch for catastrophic backtracking on nested quantifiers — a common ReDoS source. The tool caps match counts to keep the page responsive on pathological patterns.
matchgroupshighlightReDoS-saferun · outputregen · matchesRefresh -> new 10matches · livegroups · live - 04
Copy or export
Grab the output as JSON, CSV, or plain text — ready for your editor or pipeline.
Copy writes via navigator.clipboard.writeText; downloads use a Blob and object URL, so nothing transits the network and the output is byte-identical to what you see on screen.
copyexportclipboardblobexport · exportedready · savedCopiedready to shipsuccess
Regex patterns that don't melt down
Use named groups
(?<year>\d{4}) reads better than $1 and survives reordering. Supported in ECMAScript 2018+.
Anchor strictly
Use ^/$ with the m flag when matching whole lines. Without anchors, partial matches sneak through.
Avoid catastrophic backtracking
Nested quantifiers like (a+)+ can explode. Run patterns through ReDoS Detector first.
Escape every literal
Backslash any meta character you want literally: \.\$\^\*\+\?\(\)\[\]\{\}\|\\.
Test edge cases
Empty string, single character, unicode, the maximum length you expect — write fixtures for each.
Patterns aren’t parsers
Don’t parse HTML, JSON, or balanced parens with regex. Use a proper parser when the grammar is recursive.
When to reverse a regex
Synthesize fixtures, fuzz inputs, or eyeball intent.
Fixtures
Generate ID strings for tests, seeded by your regex. Compiles through the JavaScript RegExp constructor — engine quirks (Unicode property escapes, sticky matching, named groups) work when their flags are on. Error messages cite the exact position of any syntax issue.
ReDoS-safeDemo data
Fill demos with plausible-looking codes. Pairs with the ReDoS detector to catch catastrophic backtracking before you deploy. A pattern that handles 1k-character input fine can become a denial-of-service vector on attacker-controlled 1M-character input.
ECMA-compliantFuzz inputs
Throw varied matching strings at your validators. Output exports as JavaScript, Python re, Java util.regex, .NET System.Text.RegularExpressions, PCRE, and POSIX — language quirks are highlighted on conversion so you don't ship a JS-only pattern to a Go service.
spec-gradeVerify intent
Eyeball the samples to confirm the regex matches what you meant. Capture groups (named or numbered) round-trip cleanly into replacement strings, JSON output, or CSV extraction without re-typing. Backreferences ($1, ${name}) preserve semantics across languages.
cross-engineTeach regex
Show students concrete strings that satisfy a pattern. Test against edge cases — empty input, single character, max length, multibyte boundaries — to catch off-by-one and zero-length match bugs before they reach production.
test-readySeed forms
Pre-fill development forms with valid values. All matching runs client-side so secret patterns never leave the browser. Useful when the pattern itself is sensitive (PII regexes, internal data formats, security filters).
production-readyFrequently asked questions
Something missing?
Tell us what you need. We ship the top requests every two weeks.