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Regular Expression Tester

Regular Expression Pattern

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Test Text

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Match Results

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Enter a regular expression pattern to start testing.

About Regex Tester

Our free online Regex Tester helps you build, test, and debug regular expressions in real-time. See matches highlighted instantly, test against sample data, and learn regex syntax with our comprehensive tool designed for developers of all skill levels.

Key Features

Real-time Matching

See matches highlighted instantly as you type your pattern.

Flag Support

Test with global (g), case-insensitive (i), multiline (m), and other flags.

Match Highlighting

Visual highlighting of all matches in your test string.

100% Client-side

All testing happens in your browser - your patterns stay private.

Match Groups

View captured groups and their positions.

Error Detection

Invalid regex syntax is caught and explained.

How to Use

  1. 1Enter your regular expression pattern in the pattern field.
  2. 2Add test string(s) in the test area.
  3. 3Enable flags (g, i, m, etc.) as needed.
  4. 4View highlighted matches and captured groups instantly.

Pro Tips

  • 💡Start simple - build your regex incrementally and test each step.
  • 💡Use the 'g' flag to find all matches, not just the first one.
  • 💡Escape special characters (. * + ? etc.) when matching them literally.
  • 💡Use character classes [a-z] instead of alternation (a|b|c...) when possible.

Frequently Asked Questions

What is a regular expression?
A regular expression (regex) is a pattern that describes a set of strings. It's used for searching, matching, and manipulating text based on patterns.
What do the flags mean?
g = global (find all matches), i = case-insensitive, m = multiline (^ and $ match line boundaries), s = dotall (. matches newlines).
Why doesn't my regex match?
Common issues: forgetting to escape special characters, missing the 'g' flag, or the pattern being too specific. Test with simpler patterns first.
How do I match special characters?
Escape them with a backslash: \. for period, \* for asterisk, \( \) for parentheses, etc.