Developer Tools

Online Regex Tester & Visualizer

Build and test JavaScript regular expressions against sample text with live matches, capture groups, flags, and highlighting.

How to use this tool

  1. Enter a regular expression pattern.
  2. Choose JavaScript flags such as g, i, m, s, u, or y.
  3. Paste sample text into the test string editor.
  4. Review highlighted matches and capture group details.
  5. Copy the final regex when the pattern behaves as expected.

Examples

  • Test an email or URL pattern before using it in form validation.
  • Extract IDs, dates, or log fields from a sample line.
  • Compare match behavior with and without the global or ignore-case flags.

Important concepts

  • The g flag returns all matches instead of stopping after the first one.
  • Capture groups return parts of a match for extraction or replacement.
  • Character classes such as \d, \w, and \s match common character groups.
  • Anchors such as ^ and $ control where a pattern can match.

Common problems

  • Forgetting to escape special characters such as dots in domain names.
  • Using a greedy quantifier when a narrower match is needed.
  • Expecting JavaScript regex to support features from another regex flavor.
  • Testing against too little sample data.

Frequently asked questions

Which regex flavor does this tool use?

The tester uses JavaScript regular expressions, so behavior should match modern browser JavaScript regex support.

Why does a regex work elsewhere but not here?

Different languages support different regex features. Check whether the pattern uses syntax that JavaScript does not support.

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