Regex Tester
Test and validate regular expressions
Regex Tester
How to Use
- Enter your regex pattern in the input field
- Select flags (g, i, m, s, u, y) as needed
- Enter test string to match against
- Click "Test Regex" to see matches and capture groups
- Use common patterns as starting templates
Privacy Notice
This tool runs entirely in your browser. No data is sent to any server. All regex testing is performed locally using JavaScript's RegExp engine.
Your Privacy is Protected
All processing happens entirely in your browser. No data is stored, transmitted, or tracked. Your information remains completely private and secure on your device.
About Regex Tester
Test and validate regular expressions (regex) with our interactive regex tester. Regular expressions are powerful patterns for searching, matching, and manipulating text - essential for developers, data analysts, and anyone working with text processing. Our tool provides real-time pattern matching, highlights matches in test strings, explains regex syntax, shows capture groups, supports all regex flags, and includes a library of common regex patterns. Perfect for debugging regex patterns, learning regex syntax, validating user input patterns, extracting data from text, and testing search/replace operations before implementing in code.
Key Features
Real-Time Pattern Matching
See matches highlighted instantly as you type regex and test strings. Immediate visual feedback for pattern debugging.
All Regex Flags
Support for global (g), case-insensitive (i), multiline (m), sticky (y), unicode (u), and dotall (s) flags.
Capture Group Display
Shows all capture groups and their matches. Essential for understanding complex patterns with parentheses.
Pattern Library
Pre-built patterns for emails, URLs, phone numbers, dates, and more. Learn from examples and customize for your needs.
Syntax Explanation
Breaks down regex pattern to explain what each part does. Educational tool for learning regex.
Find and Replace Testing
Test replacement patterns before using in code. Preview how replace operations modify text.
How to Use Regex Tester
Enter your regular expression pattern in the regex field
Enter your regular expression pattern in the regex field. Follow the tool interface to complete this step.
Add test text or sample strings to match against
Add test text or sample strings to match against. Follow the tool interface to complete this step.
Select appropriate flags (global, case-insensitive, etc.)
Select appropriate flags (global, case-insensitive, etc.). Follow the tool interface to complete this step.
View highlighted matches and capture groups instantly
View highlighted matches and capture groups instantly. Follow the tool interface to complete this step.
Adjust pattern until it matches exactly what you need
Adjust pattern until it matches exactly what you need. Follow the tool interface to complete this step.
Test edge cases to ensure pattern works correctly
Test edge cases to ensure pattern works correctly. Follow the tool interface to complete this step.
Copy working regex pattern for use in your code
Copy working regex pattern for use in your code. Follow the tool interface to complete this step.
Frequently Asked Questions
What is regex and why use it?
Regex (regular expressions) is a powerful pattern-matching language for text. Use it for validation (email format), searching (find all URLs), extraction (get all dates), and replacement (modify text patterns). More powerful than simple string matching.
What do regex flags do?
Flags modify pattern behavior: g (global) finds all matches not just first, i (case-insensitive) ignores case, m (multiline) makes ^ and $ match line breaks, s (dotall) makes . match newlines, u (unicode) enables unicode support.
What are capture groups?
Parentheses () create capture groups that extract matched portions. Example: (\d{3})-(\d{4}) captures area code and number separately from 555-1234. Access captured groups in code for data extraction.
How do I match special characters literally?
Escape special characters with backslash: \. matches literal period, \* matches asterisk, \( matches parenthesis. Special characters: . * + ? ^ $ { } [ ] \ | ( )
What's the difference between * and +?
* matches zero or more occurrences (a* matches '', 'a', 'aa'). + matches one or more (a+ matches 'a', 'aa' but not ''). Use + when pattern must appear at least once.
How do I test regex for different programming languages?
Core regex syntax is similar across languages, but some features vary. JavaScript, Python, Java, and C# have slight differences. Test with flags and syntax specific to your target language's regex engine.
What does ^ and $ mean?
^ matches start of string (or line in multiline mode). $ matches end of string (or line). ^test$ matches only 'test', not 'testing' or 'attest'. Use for exact matching.
How do I match optional characters?
Use ? after a character or group for optional: colou?r matches both 'color' and 'colour'. (https?)? matches optional 's' in http(s).
Use Cases
- Form Validation: Create and test patterns for email validation, phone number formats, password requirements, ZIP codes, and more. Ensure user input matches required formats.
- Data Extraction: Extract specific information from logs, documents, or datasets. Find emails, URLs, dates, numbers, or custom patterns in large text files.
- Search and Replace: Test complex find-and-replace operations before running on production data. Preview how regex replacements modify text.
- Log File Analysis: Parse server logs, application logs, or system logs. Extract timestamps, error codes, IP addresses, or custom log data.
- Text Processing Scripts: Develop and debug regex for Python, JavaScript, Java, or any language. Test patterns before implementing in code.