Regex String Generator
Create reproducible synthetic strings from common regular-expression tokens. Unsupported constructs are reported instead of being executed.
Also known as: regexp generator · pattern string · regex test data
seeded · synthetic data
Output
About this tool, tips & examples
What it does
The Regex String Generator runs regular expressions backwards: give it a pattern and it produces strings that match. It parses a safe, documented subset of regex syntax itself — never executing your pattern through the platform’s regex engine — and generates up to 1,000 seeded, reproducible matches per run.
Supported syntax
Literals, | alternation, groups, ., character classes like [A-Z],
the escapes \d, \w, \s, and the quantifiers ?, *, +, and
{m,n}. Anchors (^, $) are accepted as zero-width markers.
Unsupported constructs — lookarounds, backreferences, flags, advanced
Unicode — are reported in the pattern field instead of being
silently mishandled.
Common use cases
- Form validation fixtures — generate strings matching your
validation pattern to test the accept path (
[A-Z]{2}\d{4}→ license-plate-shaped values). - Parser test data — inputs guaranteed to match a grammar fragment.
- API examples — format-correct IDs, codes, and references for documentation.
- Fuzzing seed corpora — pattern-conforming strings as starting points for mutation-based fuzzers.
Settings
- Regex pattern — the pattern to generate from, in the supported subset.
- How many — 1 to 1,000 matching strings, exportable as text, CSV, or JSON.
- Seed — the same seed and pattern regenerate the identical strings.
Privacy note
Patterns are parsed and strings generated locally in your browser; nothing is uploaded. Generated values are synthetic — even when a pattern describes something sensitive-looking, the output is random material, not real credentials or identities.
FAQ
Does this execute my regex? No — it parses only the documented subset with its own safe parser, so there’s no pathological-regex blowup and no engine quirks. That’s also why exotic constructs are rejected rather than guessed at.
Why was my pattern rejected? It uses a feature outside the subset (lookaround, backreference, flags). Rewrite with literals, groups, classes, and the supported quantifiers — most fixture patterns fit comfortably.
How do unbounded quantifiers behave?
* and + generate bounded repetitions internally, so output stays a
sensible length. Pin exact lengths with {m,n} when the size matters.