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Regex tester

Test your regular expressions live

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Flags

Build and debug your regular expressions without leaving the browser: type a pattern, toggle the flags (g i m s u y) and instantly see every match highlighted inside your test text. Perfect for validating an e-mail format, extracting fields from a log, checking a validation rule or previewing a find & replace before running it in your editor. Captured groups — numbered and named ((?<name>…)) — are listed match by match, and replace mode applies $1, $<name> live.

Everything runs locally in your browser: neither your pattern nor your text is ever sent to a server. No tracking, no ads, and it works offline. A safety guard truncates the test text to 50,000 characters to keep a costly regex (ReDoS) from freezing the tab.

FAQ

Which regex syntax is used?
JavaScript's (native <code>RegExp</code> object). Named groups <code>(?&lt;name&gt;…)</code>, lookbehind and the <code>s</code> (dotall) and <code>u</code> (unicode) flags are supported depending on your browser.
How does replacement work?
Tick “Replace mode”, type the replacement with <code>$1</code>, <code>$2</code> or <code>$&lt;name&gt;</code> to reuse captured groups. The <code>.replace()</code> result is shown live and can be copied.
Why is my text truncated?
Beyond 50,000 characters the test text is cut: some regexes can become exponentially slow (ReDoS) and freeze the tab. This limit keeps the tool responsive.
Is my data sent anywhere?
No. Everything runs in your browser, nothing is sent or stored. No tracking, no ads, and it works offline.