# Regex Tester

Canonical: https://herebetools.com/regex

Test and debug regular expressions

Write and test regex patterns against your input with live match highlighting as you type. All JavaScript flags are supported: global (g), case-insensitive (i), multiline (m), dotAll (s), and Unicode (u). Capture groups and named capture groups are shown individually. Use replace mode to preview substitutions before applying them in code. Useful for validating emails, parsing log files, and building input validation patterns.

## Questions and answers

### Which regex engine does the tester use?

The tester uses the JavaScript RegExp engine built into your browser, so results match exactly what you would see in JavaScript code.

### Are lookaheads and lookbehinds supported?

Yes, modern regex features including lookaheads, lookbehinds, and named capture groups are supported in all modern browsers.

## Related tools

- [String Inspector](https://herebetools.com/string-inspect): Analyze text: bytes, entropy, frequency, encoding detection
- [Escape / Unescape](https://herebetools.com/escape): Escape and unescape HTML, JS, JSON, and URL strings
- [URL Encode](https://herebetools.com/url-encode): Percent-encode and decode URLs and query strings

Tool processing runs in your browser.

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