Free Online Regex Tester & Debugger

Test regular expressions with live matching and highlighting. Includes common regex presets for email, URL, phone and IP validation. Free online regex tool.

What Is Online Regex Tester & Debugger?

Regular expressions (regex) are patterns used to match, search and manipulate text. They are one of the most powerful tools in programming, used for everything from form validation to log parsing. However, regex syntax is notoriously difficult — a misplaced quantifier or forgotten escape character can change the meaning of an entire pattern.

A regex tester lets you write patterns and see matches highlighted in real time against your test string. This immediate visual feedback makes it far easier to build and debug complex patterns than writing them blindly in code and running your application to see if they work.

How to Use This Tool

  1. Enter your regex pattern in the pattern field at the top.
  2. Type or paste your test string in the text area below.
  3. Matches are highlighted in real time as you type the pattern.
  4. Toggle flags (global, case-insensitive, multiline) using the flag buttons.
  5. Try the preset patterns for common validations like email, URL or phone number.

Tips & Best Practices

  • Start simple and build up — test each part of your pattern individually before combining them.
  • Remember that regex is greedy by default. Use ? after quantifiers (.*?) for non-greedy matching.
  • Escape special characters (. * + ? [ ] { } ( ) ^ $ | \) with a backslash when you want to match them literally.
  • Use the global flag (g) to find all matches, not just the first one.
  • Test edge cases: empty strings, very long input, special characters and Unicode text.

Common Use Cases

  • Building and testing email, phone number or postcode validation patterns.
  • Extracting specific data from log files or CSV data.
  • Creating search-and-replace patterns for text editors and code refactoring.
  • Validating user input format in web forms before submission.
  • Parsing structured text like dates, URLs or file paths.

Frequently Asked Questions

How do I test a regex pattern?

Enter your regex pattern in the pattern field, type your test string below, and matches are highlighted in real time. Use the flag toggles for global, case-insensitive or multiline matching.

Are there prebuilt regex patterns?

Yes. The tool includes presets for common patterns like email validation, URL matching, phone numbers and IP addresses. Click any preset to load it instantly.