Regex Tester & Explainer
Free online regex tester with visual step-by-step explanation. Test patterns, see matches highlighted, and understand what each part does.
Test and debug your regular expressions with our free online regex tester. See matches highlighted in real-time and get a visual explanation of what each part of your pattern does.
All processing happens in your browser. Your test data never leaves your device, ensuring complete privacy.
How to Use This Tool
- 1 Enter your regex pattern in the first field
- 2 Add flags like 'g' (global) or 'i' (case-insensitive)
- 3 Enter test text to match against
- 4 See matches highlighted in the output
- 5 Review the pattern explanation to understand each part
Use Cases
Form Validation
Test email, phone, and other validation patterns before implementing.
Data Extraction
Build patterns to extract specific data from text or logs.
Search & Replace
Develop complex search patterns for text editors or code.
Text Processing
Create patterns for cleaning, formatting, or transforming text data.
Frequently Asked Questions
What are regex flags?
Flags modify how the pattern matches: 'g' finds all matches, 'i' makes it case-insensitive, 'm' makes ^ and $ match line boundaries, 's' makes . match newlines.
Why isn't my pattern matching?
Common issues: forgetting to escape special characters (. * + ? need \), missing the global flag 'g' for multiple matches, or case sensitivity (add 'i' flag).
What's the difference between * and +?
* matches zero or more occurrences (optional), while + requires at least one match. For example, a* matches '' and 'aaa', but a+ only matches 'a' or more.
How do capture groups work?
Parentheses () create capture groups that extract parts of matches. Group 1 is the first (), Group 2 is the second, etc. Access them in match results.
Is this regex flavor compatible with my language?
This tester uses JavaScript regex. Most patterns work across languages, but some features like lookbehind vary. Always test in your target environment.