Regex Tester – Test and Debug Regular Expressions
Regular expressions are powerful but can be tricky to get right. The Regex Tester provides an interactive environment to test regular expressions against sample text, see matches in real-time, and experiment with different flags. Perfect for learning regex, debugging patterns, or validating expressions before using them in your code.
With support for regex flags, live matching, and a pattern library, this tool helps you build, test, and refine regular expressions quickly and easily.
How Regular Expressions Work
Regular expressions (regex) are pattern-matching strings that describe search patterns in text. They use special characters and syntax to match specific text patterns, making them powerful tools for:
- Text validation
- Search and replace operations
- Data extraction
- Input parsing
Regex Flags Explained
Global (g)
Find all matches, not just the first one. Without this flag, regex stops after finding the first match.
Case Insensitive (i)
Makes the pattern case-insensitive. "ABC" will match "abc", "Abc", "ABC", etc.
Multiline (m)
Allows ^ and $ to match line breaks. Treats each line as a separate string.
Unicode (u)
Enables Unicode matching, allowing matching of Unicode characters.
Sticky (y)
Matches only from the position indicated by the lastIndex property.
Common Regex Patterns
- Email:
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ - URL:
^https?://[^\s/$.?#].[^\s]*$ - Phone:
^\+?[\d\s\-\(\)]+$ - Numbers Only:
^\d+$
Testing Best Practices
- Test Edge Cases: Test with various inputs, including edge cases
- Use Flags Appropriately: Understand what each flag does
- Validate Matches: Ensure matches are what you expect
- Test Negatives: Verify patterns reject unwanted matches
Conclusion
The Regex Tester is an essential tool for working with regular expressions. By providing live matching, flag support, and instant feedback, it helps you build and debug regex patterns efficiently.