Regex Tester
Test a regular expression against real text.
Runs entirely in your browser — your data is never uploaded to any server.
How it works
- Write your patternJavaScript regular expression syntax.
- Add test textPaste a realistic sample.
- Review the matchesPositions and capture groups included.
What this tool does
- All JavaScript flags including sticky and unicode
- Capture groups and named groups listed per match
- Optional replacement preview
- Execution guard against runaway patterns
Frequently Asked Questions
JavaScript, as implemented by your browser. Most syntax is shared with other languages, though lookbehind and named group support vary elsewhere.
Without the global flag, matching stops at the first result. Add g to find them all.
It previews the result of a replace operation. Use $1, $2 to insert capture groups.
Nested quantifiers on overlapping alternatives can backtrack exponentially. The tool stops after a safety limit and tells you.
Privacy and security
Your input is processed by JavaScript running inside your browser. Nothing you paste is sent over the network, logged, or stored — which is what makes this safe to use with production data. If you want to check this yourself: open your browser’s developer tools, switch to the Network tab, and use the tool — you will see no request carrying your file or input leave the page.
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