Regex Tester & Pattern Builder
Test regular expressions with real-time matching and highlighting. Build and validate regex patterns with our interactive tester featuring common examples and detailed match information.
Test String
Results (0 matches)
Highlighted Matches:
Regex Quick Reference
Character Classes
- . - Any character
- \\d - Any digit [0-9]
- \\w - Word character [A-Za-z0-9_]
- \\s - Whitespace
- [abc] - Any of a, b, or c
- [^abc] - Not a, b, or c
Quantifiers
- * - 0 or more
- + - 1 or more
- ? - 0 or 1
- {3} - Exactly 3
- {3,} - 3 or more
- {3,5} - Between 3 and 5
Anchors
- ^ - Start of string
- $ - End of string
- \\b - Word boundary
- \\B - Not word boundary
Groups
- () - Capturing group
- (?:) - Non-capturing group
- | - OR operator
- \\ - Escape character
How to Use the Regex Tester
Simple 5-Step Process
- 1Enter your regular expression pattern in the pattern field
- 2Select appropriate flags (global, case-insensitive, multiline, etc.)
- 3Input your test string in the test area
- 4Click "Test Regex" to see real-time matching and highlighting
- 5Review match details, groups, and export results if needed
Pro Tips
- Start simple: Begin with basic patterns and add complexity gradually
- Use examples: Load common patterns from our examples library
- Test edge cases: Include various input types in your test string
- Escape special chars: Use backslashes to escape special characters
- Use capturing groups: Parentheses help extract specific parts
Common Regex Use Cases
Data Validation
Validate user input like email addresses, phone numbers, passwords, and credit card numbers in forms and applications.
Text Processing
Extract information from logs, parse CSV files, clean data, and transform text formats in bulk processing tasks.
Search & Replace
Find and replace complex patterns in code, documents, and databases using advanced pattern matching.
Web Scraping
Extract structured data from HTML pages, parse API responses, and collect information from web sources.
Security & Filtering
Filter malicious content, validate input security, and implement content moderation systems.
Log Analysis
Parse server logs, extract error patterns, monitor system events, and analyze application performance.
Regex Learning Guide
Basic Patterns
Quantifiers
Advanced Features
Common Mistakes
- • Forgetting to escape special characters like . + * ? ^ $ | ( ) [ ] \\
- • Using greedy quantifiers when lazy ones are needed (use ? after quantifiers)
- • Not considering edge cases like empty strings or special characters
- • Overcomplicating patterns - start simple and build complexity gradually
- • Forgetting to anchor patterns with ^ and $ when exact matches are needed
Frequently Asked Questions
What is a regular expression (regex)?
A regular expression is a sequence of characters that defines a search pattern. It's used for pattern matching, text validation, data extraction, and string manipulation across programming languages and text editors.
What are regex flags and how do they work?
Regex flags modify how the pattern matching works. Common flags include: g (global - find all matches), i (case-insensitive), m (multiline - ^ and $ match line boundaries), s (dot matches newlines), u (Unicode support), and y (sticky - match at exact position).
How do I test if my regex pattern is working correctly?
Enter your regex pattern in the pattern field, add your test text, and click "Test Regex". The tool will highlight matches in real-time and show detailed information about each match, including position and captured groups.
What are capturing groups in regex?
Capturing groups, denoted by parentheses (), allow you to extract specific parts of a match. For example, in the pattern (\d+)-(\w+), the first group captures digits and the second captures word characters. Our tool shows all captured groups for each match.
Can I save my regex test results?
Yes, click the "Export Results" button to download a JSON file containing your pattern, test string, all matches, and their details. This is useful for documentation and sharing test cases.
What's the difference between greedy and non-greedy matching?
Greedy matching (default) tries to match as much as possible, while non-greedy (lazy) matching tries to match as little as possible. Use ? after quantifiers (* + {}) to make them non-greedy. For example, .*? matches as few characters as possible.