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Test your regular expressions with live highlighting

Regular expressions (regex) are a powerful tool for pattern matching and text manipulation, but they can be challenging to master. Our free online Regex Tester makes it easy to create, test, and debug regular expressions with real-time feedback and helpful features.

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Test your regular expressions with live highlighting

What is a Regex Tester?

A Regex Tester is an interactive tool that allows you to:

  • Write and test regular expressions in real-time
  • See matches highlighted in your test text
  • Toggle between different regex flags (global, case-insensitive, multiline)
  • View detailed match information and capture groups
  • Test replacement patterns
  • Access common regex patterns and a built-in cheat sheet

How to Use the Regex Tester

  1. Enter your regular expression in the pattern input field
  2. Type or paste text to test against in the test string area
  3. Toggle flags (g, i, m) as needed
  4. View matches in real-time with highlighting
  5. Navigate between matches using the arrow buttons
  6. Switch to Replace mode to test replacement patterns

Common Regex Patterns

Email Address

\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b

URL

https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)

Phone Number

\+?\d{1,4}?[-.\s]?\(?\d{1,3}?\)?[-.\s]?\d{1,4}[-.\s]?\d{1,4}[-.\s]?\d{1,9}

Date (YYYY-MM-DD)

\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])

Advanced Features

Using Capture Groups

Capture groups allow you to extract specific parts of a match. For example, to extract the domain from an email:

^[^@]+@([^@]+)$

Lookaheads and Lookbehinds

Lookaheads and lookbehinds let you match patterns that are followed by or preceded by another pattern:

  • Positive lookahead: X(?=Y) - Match X only if followed by Y
  • Negative lookahead: X(?!Y) - Match X only if not followed by Y
  • Positive lookbehind: (?<=Y)X - Match X only if preceded by Y
  • Negative lookbehind: (?<!Y)X - Match X only if not preceded by Y

Replacement Patterns

In replace mode, you can use special replacement patterns:

  • $& - The matched text
  • $1, $2, etc. - Captured groups
  • $` - Text before the match
  • $' - Text after the match

Common Pitfalls

  1. Greedy vs. Lazy Matching

    • Greedy: .* matches as much as possible
    • Lazy: .*? matches as little as possible

  2. Escaping Special Characters Remember to escape special regex characters: . * + ? ^ $ { } ( ) | [ ] \ /

  3. Performance Issues Some patterns can cause catastrophic backtracking. If the tester becomes slow, try:

    • Making your patterns more specific
    • Using atomic groups: (?>...)
    • Avoiding nested quantifiers when possible

Tips and Tricks

  • Use the built-in cheat sheet for quick reference
  • Test with different flags to see how they affect matching
  • Start with simple patterns and build up complexity
  • Use the preset patterns as a starting point
  • The tool automatically escapes special characters in the replacement string

Conclusion

Our Regex Tester makes it easy to create, test, and debug regular expressions. Whether you’re a beginner learning regex or an experienced developer working with complex patterns, this tool will help you get the job done faster and with fewer errors.

Try it now by entering your own patterns in the tester above, or explore the built-in examples to learn more about regular expressions.

Need Help?

If you have any questions or run into issues, feel free to leave a comment below or contact our support team. Happy pattern matching!