Regex Tester
Test regular expressions live: highlight every match as you type, inspect capture groups and debug patterns for JavaScript, with common flags one click away.
0 match(es)
This tool runs entirely in your browser. Your data never leaves your device — it is not uploaded to any server.
How to use
- 1Enter your regular expression in the pattern field.
- 2Toggle flags (g, i, m, s, u) and paste your test string.
- 3Read the highlighted matches and the list of groups; adjust the pattern until it captures exactly what you need.
Regex Tester
Type a pattern, flip the flags you need (global, case-insensitive, multiline, dotAll, unicode) and paste your test string — every match is highlighted in place while a list below shows each match with its index and capture groups, named groups included.
Invalid patterns are reported immediately with the parser's own message instead of a broken page, and zero-length matches are handled safely, so patterns like a* behave the way your runtime would.
Frequently asked questions
Which regex flavor does this use?
JavaScript (ECMAScript) RegExp — the same engine that runs in your browser and Node. Patterns for PCRE, Python or Java are usually compatible, but lookahead/lookbehind and unicode handling can differ slightly.
Why does my pattern match strange empty positions?
Patterns that can match an empty string (like a* or (?:)?) produce zero-length matches. The tester advances one character after each, exactly like JavaScript's own iteration does.
Is my test data sent anywhere?
No. Matching runs live in your browser — nothing is uploaded or stored.
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Embed this tool
Put this tool on your own site with one line — it runs entirely in the visitor's browser.
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