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Regex Tester

Test regular expressions

About Regex Tester

Regex Tester runs your pattern against JavaScript's native RegExp engine, entirely in your browser — nothing is uploaded to a server. It only tests JavaScript regex syntax; there's no flavor selector for Python, PHP, Java, or other engines, no match highlighting within the text, no explanation panel, and no saved pattern library — just a match count and a list of matched substrings.

How to use Regex Tester

  1. 1Type or paste your regex pattern into the Pattern field.
  2. 2Set flags (e.g. gi for global, case-insensitive) in the Flags field.
  3. 3Paste the text you want to test into the text area.
  4. 4Click 'Test' to see whether it matches, how many matches were found, and each matched substring.

Frequently Asked Questions

What is a regular expression?

A pattern-matching syntax used to search, validate, or extract text based on rules rather than exact strings.

Which regex flavors does it support?

Only JavaScript's native regex syntax — there's no flavor selector for Python, PHP, Java, .NET, or Perl.

Does it highlight matches within my text?

No — matched substrings are listed separately below the result, not highlighted inline within the test text.

Can I save my regex patterns?

No, there's no save feature or pattern library — copy patterns elsewhere if you want to keep them.

Tips & Tricks

  • ✓Use the g flag to see every match rather than stopping at the first one.
  • ✓If your pattern throws an error, check for unescaped special characters or unbalanced parentheses/brackets.
  • ✓Since only JavaScript regex syntax is supported, patterns relying on features specific to other languages (like Python's named groups syntax) may behave differently or fail.
  • ✓Test with a range of inputs, including edge cases and empty strings, to confirm your pattern behaves as expected.