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Regex Tester

Test and debug regular expressions in real-time. See matches highlighted instantly with capture groups.

What is a Regex Tester?

A regex tester lets you write, test, and debug regular expressions against sample text in real time. Regular expressions (regex) are powerful pattern-matching tools used in virtually every programming language for validation, search, extraction, and text transformation.

Our online regex tester highlights matches instantly as you type, shows capture groups, and helps you understand exactly what your pattern matches. It’s faster than writing test code and invaluable for getting complex patterns right before putting them in production.

How to Use This Regex Tester

  1. Enter your regular expression in the pattern field
  2. Set flags like global (g), case-insensitive (i), or multiline (m)
  3. Paste your test text in the input area
  4. See matches highlighted in real time as you modify the pattern
  5. Review capture groups to verify your parenthesized sub-patterns work correctly

Common Use Cases

  • Form validation — Test email, phone number, or URL validation patterns before implementing them
  • Log parsing — Extract timestamps, IP addresses, or error codes from log files
  • Search and replace — Build complex find-and-replace patterns for code refactoring
  • Data extraction — Pull specific fields from unstructured text (scraping, ETL)
  • Input sanitization — Test patterns that strip or escape dangerous characters

Frequently Asked Questions

What’s the difference between .* and .*? in regex?

.* is greedy — it matches as many characters as possible. .*? is lazy (non-greedy) — it matches as few characters as possible. For example, with the text <b>hello</b>, the pattern <.*> matches the entire string, while <.*?> matches just <b>.

How do I match a literal dot or other special character?

Escape it with a backslash: \. matches a literal dot, \$ matches a dollar sign. Special regex characters that need escaping include: . * + ? ^ $ { } [ ] ( ) | \

What are capture groups and when should I use them?

Capture groups (parentheses) extract specific parts of a match. For example, (\d{4})-(\d{2})-(\d{2}) matching 2024-01-15 gives you three groups: year, month, and day. Use them when you need to extract or rearrange parts of matched text.