What this tool does
Regular expressions are compact, powerful and easy to get subtly wrong. This tester runs your pattern against a sample as you type, highlights every match, lists capture groups and previews replacements. Flags follow JavaScript RegExp semantics, including lookbehind and named groups.
How to use it
- Enter the pattern and flags.
- Paste the test string and inspect highlighted matches.
- Add a replacement to preview the transformed text.
Questions
Which regex flavor is used?
JavaScript (ECMAScript). Most syntax is shared with PCRE, Java and Python, but lookbehind and Unicode property escapes vary.
Why do zero-length matches appear?
Patterns such as ^, $ or word boundaries match a position, not characters. The tester advances one character to avoid an infinite loop.
Is my text sent anywhere?
No. Matching happens in this page.