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Regex Tester

Test regular expressions and see every match highlighted.

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  • Works in Your Browser

Regex tester

Test regular expressions live

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How to use the regex tester

Three steps, all in your browser.

  1. 1

    Enter a pattern

    Type a regular expression and the text to test it against.

  2. 2

    Read the result

    Matches, differences or the explanation update as you type.

  3. 3

    Copy the result

    Copy the output in one click. Nothing is saved or sent anywhere.

Regex Tester: what to know

The regex tester runs your regular expression against sample text as you type and highlights every match, with the capture groups for each one, including named groups. It can also preview a replacement and explain the pattern piece by piece. It uses the JavaScript (ECMAScript) engine built into your browser, so what matches here matches in JavaScript and TypeScript code.

Flags change how the pattern is applied: g finds all matches rather than just the first, i ignores case, m makes ^ and $ match at the start and end of each line, s lets the dot match line breaks, and u turns on full Unicode support, including \p{L}-style property escapes. Most syntax (character classes, quantifiers, groups, lookahead) works the same in PCRE, Python, Java and .NET, but details differ, so check in your target language too.

Watch for catastrophic backtracking: nested quantifiers such as (a+)+ or (.*)* can take exponential time on input that almost matches, which can freeze a page or a server (a regular expression denial of service). Here the pattern runs in a background worker and is stopped if it takes too long, so the page stays responsive; in your own code, keep quantifiers specific and anchor patterns with ^ and $ when you mean to match the whole string.

Popular uses

  • Building validation patterns for forms
  • Writing search-and-replace patterns for code
  • Extracting fields from log lines
  • Debugging why a pattern does or doesn't match

Tips for the best result

  • Start with a small pattern that matches and extend it step by step.
  • Escape special characters such as . * + ? ( ) [ ] { } | \ ^ $ with a backslash to match them literally.
  • See the regex cheat sheet in the reference section for syntax at a glance.

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Frequently asked questions