Browser-only tool
Regex tester
Enter a JavaScript regular expression and sample text to inspect matches, groups, and flags locally in the browser.
Warning: complex regex patterns can be slow or unsafe on large input. JavaScript regex behavior can differ from other languages.
Privacy And Limitations
Patterns and sample text are processed locally in your browser and are not uploaded.
- This page uses JavaScript RegExp behavior; other languages can differ.
- Complex patterns can hang or perform badly on large input.
- Do not run untrusted regex patterns against large sensitive datasets without safeguards.
FAQ
Which regex flavor is used?
The browser JavaScript RegExp engine is used, so behavior can differ from PCRE, Python, Java, or .NET.
What is ReDoS?
ReDoS is a denial-of-service risk caused by regex patterns with catastrophic backtracking on certain inputs.
Can this replace production tests?
No. It is useful for exploration, but production patterns should be tested in the same runtime as the app.
Are sample texts uploaded?
No. Matching runs locally in the browser.
Why do flags matter?
Flags such as g, i, m, s, u, and y change matching behavior and output.