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Regex Tester

The Regex Tester is a free online tool that runs a regular expression against sample text and highlights every match and capture group live as you type. It uses your browser's native JavaScript RegExp engine, so patterns and test data are never uploaded to a server.

Last updated · Free, no signup

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What does a regular-expression tester do?

A regex tester applies a regular expression to sample text and highlights each match while exposing capture groups and flag behavior. It shortens the edit-and-run cycle when building validators, search patterns, replacements, or log filters because changes can be checked against representative input immediately.

Patterns are evaluated by the browser's ECMAScript RegExp engine with the g, i, m, s, u, and y flags. Results therefore follow JavaScript syntax and browser capabilities; constructs copied from PCRE, Python, Java, or .NET may behave differently or fail even when they are valid in their original engine.