Regex Tester & Debugger

A regex tester is an essential tool for developers working with regular expressions (regex or regexp). Our online regex tester provides real-time pattern matching, syntax validation, match highlighting, and capture group visualization to help you build and debug regex patterns efficiently.

What are Regular Expressions?

Regular expressions are sequences of characters that define search patterns. They're used for:

• Validation: Email, phone numbers, passwords, credit cards
• Search: Find specific patterns in text
• Replace: Find and replace text based on patterns
• Extraction: Extract specific information from strings
• Parsing: Break down complex strings into components

Key Features

• Real-Time Testing: See matches as you type your pattern
• Match Highlighting: Visual highlighting of matched text
• Capture Groups: Display captured groups for each match
• Multiple Flags: Support for g, i, m, and s flags
• Match Position: See exact position of each match
• Pattern Examples: Pre-built patterns for common use cases
• Syntax Validation: Instant feedback on invalid patterns
• Match Counter: Total count of matches found

Understanding Regex Flags

• g (global): Find all matches, not just the first one
• i (case-insensitive): Ignore uppercase/lowercase differences
• m (multiline): ^ and $ match start/end of each line
• s (dotAll): Dot (.) matches newline characters

Common Regex Patterns

Regex Syntax Reference

How to Use the Regex Tester

1. Enter your regex pattern in the pattern input field
2. Select appropriate flags (g, i, m, s) based on your needs
3. Enter or paste your test string in the test area
4. View real-time matches with highlighting
5. Check match details, positions, and capture groups
6. Use example patterns to learn common regex use cases
7. Copy your regex pattern with flags for use in code

Common Use Cases

• Form Validation: Validate user input in web forms
• Data Extraction: Extract specific data from logs or text
• Search & Replace: Find and replace patterns in text editors
• URL Routing: Match routes in web applications
• Log Parsing: Parse and analyze log files
• Data Cleaning: Clean and standardize data formats
• Security: Detect malicious patterns or SQL injection

Best Practices

• Start simple and add complexity gradually
• Test with multiple examples, including edge cases
• Use capture groups to extract specific parts
• Avoid overly complex patterns when simpler ones work
• Use non-capturing groups (?:) when you don't need to capture
• Be aware of performance with large text and complex patterns
• Document complex regex patterns with comments in your code