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Regex Tester

Test regular expressions online. Match patterns with flags and see results live.

How to Use Regex Tester

1

Enter your regex pattern

Type your regular expression in the pattern field. Select flags like global (g), case-insensitive (i), multiline (m), or dotAll (s) as needed.

2

Paste test text

Enter or paste the text you want to test against your regex pattern. The text can be any length and contain multiple lines.

3

Review matches

Matches are highlighted in the test text in real-time. Captured groups, match positions, and match count are displayed below for detailed analysis.

4

Refine and copy

Adjust your pattern based on the results until it matches exactly what you need. Copy the final regex for use in your JavaScript, Python, or other code.

About Regex Tester

Regex tester online — build and test regular expressions with real-time matching, color-coded highlighting, and detailed match information. This free regex testing tool shows all matches, captured groups, and their positions instantly as you type. Supports JavaScript ECMAScript regex syntax with all flags. Perfect for developing email validators, URL parsers, data extraction patterns, and form validation rules. All processing happens in your browser for complete privacy.

Key Features

  • Test regular expressions with real-time matching and instant feedback
  • Color-coded highlighting of all matches directly in the test string
  • Support for all flags: global, case-insensitive, multiline, dotAll, unicode
  • Detailed match information with captured groups and their positions
  • Common regex pattern library with examples for emails, URLs, and more
  • One-click copy of tested regex pattern ready for use in code

Frequently Asked Questions

How to test a regex pattern online for free?▾
Enter your regular expression in the pattern field and paste your test string below. Matches are highlighted in real-time as you type. All captured groups and match positions are displayed. No signup required.
How to write a regex for email validation?▾
A common email regex pattern is /^[\w.-]+@[\w.-]+\.[a-zA-Z]{2,}$/. Paste it into the tester with sample email addresses to verify it matches valid emails and rejects invalid ones.
How to use regex capture groups?▾
Wrap parts of your pattern in parentheses to create capture groups. The tester displays each captured group separately with its matched text and position in the string.
How to match across multiple lines with regex?▾
Enable the multiline (m) flag to make ^ and $ match line starts/ends. Use the dotAll (s) flag if you want the dot (.) to match newline characters as well.
How to use lookahead and lookbehind in regex?▾
Modern browsers support positive lookahead (?=...), negative lookahead (?!...), positive lookbehind (?<=...), and negative lookbehind (?<!...). Test them in the regex tester to verify behavior.
How to debug a regex that is not matching?▾
Check your flags (case-insensitive, global, multiline), verify escape characters are correct, and test with simplified patterns. The real-time highlighting shows exactly where matches occur or fail.
How to test regex for URL matching?▾
Use a URL pattern like /https?:\/\/[\w.-]+\.[a-z]{2,}[\/\w.-]*/gi and test it against sample URLs. The tester highlights all matched URLs in your test text.
How to convert regex between programming languages?▾
This tool uses JavaScript regex syntax (ECMAScript). Most patterns work across languages, but some features like named groups (?<name>...) and Unicode properties (\p{...}) may vary. Test your pattern here first.