Regex Tester
Test and debug JavaScript regular expressions online. Real-time match highlighting, capture groups, and explanation. Free regex tool for developers.
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How to Use Regex Tester
- Enter your regex pattern in the "Pattern" field (without /slashes/)
- Add flags (g, i, m, s, u, y) using the flag toggles or text input
- Type or paste your test string in the "Test String" area
- View matches highlighted in real-time
- Check the "Matches" section for detailed match information
- Adjust your pattern and see updates instantly
About Regex Tester
Test, debug, and refine your regular expressions with our free online Regex Tester. Regular expressions (regex) are powerful pattern-matching tools used for text searching, validation, and transformation. Our tester provides real-time feedback to help you craft perfect patterns.
Regex Tester Features: - Real-Time Matching: See matches highlight as you type - Capture Groups: View all captured groups with indices - Flag Support: Global (g), case-insensitive (i), multiline (m), and more - Match Details: Full match, groups, index, and input - Color-Coded Matches: Different colors for different groups - Pattern Explanation: Understand what your regex does
Supported Regex Flags: - g (Global): Find all matches, not just the first - i (Case-insensitive): Match regardless of case - m (Multiline): ^ and $ match line starts/ends - s (Dotall): Dot matches newlines - u (Unicode): Enable full Unicode support - y (Sticky): Match only from lastIndex position
Common Regex Use Cases: - Email Validation: /^[\w.-]+@[\w.-]+\.\w+$/ - Phone Numbers: /\d{3}-\d{3}-\d{4}/ - URLs: /https?:\/\/[\w.-]+/ - Dates: /\d{4}-\d{2}-\d{2}/ - HTML Tags: /<([a-z]+)[^>]*>/gi
Our regex tester uses the JavaScript RegExp engine, making it perfect for web development. All testing happens locally in your browser—your test data is never sent to any server.
Common Use Cases
Frequently Asked Questions
Which regex flavor does this tester use?
This tester uses the native JavaScript RegExp engine, which follows ECMAScript standards. It supports ES2018 features including named capture groups, lookbehind assertions, and the s (dotall) flag.
What do the flags mean?
g: match all occurrences; i: case-insensitive; m: multiline mode where ^ and $ match line boundaries; s: dot matches newlines; u: full Unicode support; y: sticky mode, matches from lastIndex only.
Why isn't my regex matching?
Common issues: forgetting the global flag for multiple matches, not escaping special characters (. needs \.), case sensitivity (use i flag), or anchor issues (^ and $ behavior in multiline mode).
How do I capture part of a match?
Use parentheses () to create capture groups. In /Hello (\w+)/, the word after Hello is captured. Named groups use (?<name>pattern). Access groups via match[1], match[2], or match.groups.name.
Can I test regex for other languages?
Most regex syntax is similar across languages, but there are differences. This tester is JavaScript-specific. Python, Java, .NET, and others may have additional features or syntax differences.
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