RegEx Tester

About RegEx Tester

The RegEx Tester is a powerful, browser-based tool for testing and debugging regular expressions. Whether you are a beginner learning regex or an advanced developer optimizing complex patterns, this tool provides instant visual feedback with live highlighting, capture group inspection, and replacement preview. All processing happens entirely in your browser with no server required.

Key Features

• Real-time Testing: See results instantly as you type your regex pattern
• Live Match Highlighting: Matches are highlighted directly in the test text
• Capture Groups: View all captured groups for each match
• Match Navigation: Jump between matches with next/previous buttons
• Replacement Preview: See how replacements will look before applying
• Regex Flags: Toggle g, i, m, s, u, y flags with descriptions
• Error Handling: Clear error messages for invalid patterns
• Regex Cheat Sheet: Quick reference for common patterns and syntax
• Example Templates: Pre-built patterns for email, phone, URL, date, IPv4, etc.
• History: Save and reload your last 20 regex tests
• Export Options: Download matches as JSON or CSV
• Keyboard Shortcuts: Ctrl+Enter to test, Ctrl+L to clear, Ctrl+/ for cheat sheet
• Large Text Support: Handle 200,000+ character inputs efficiently
• 100% Client-Side: All processing happens in your browser

How to Use

1. Enter Regex Pattern: Type your regular expression in the Pattern field. For example: type digits to match numbers.
2. Select Flags: Check the flags you need (g for global, i for case-insensitive, etc.). Hover over each flag to see its description.
3. Enter Test Text: Paste or type the text you want to test the regex against.
4. View Results: Matches appear instantly with their positions and captured groups.
5. Navigate Matches: Use Previous/Next buttons to jump between matches.
6. Test Replacements: Enter a replacement string to preview how replacements will look.
7. Export Results: Download matches as JSON or CSV for further processing.

Understanding Regular Expressions

Regular expressions (regex) are patterns used to match character combinations in strings. They are powerful tools for text processing, validation, and data extraction.

Common Use Cases

Capture Groups

Capture groups allow you to extract specific parts of a match. They are created using parentheses.

Replacement Patterns

When replacing matches, you can use special replacement patterns to reference matched text and groups.

• Dollar-ampersand - the entire matched string
• Dollar-1, Dollar-2, etc. - captured groups
• Dollar-backtick - text before the match
• Dollar-apostrophe - text after the match

Performance Tips

• Use specific patterns: Specific patterns are faster than generic ones
• Avoid backtracking: Use atomic groups or possessive quantifiers when possible
• Test with realistic data: Use actual data similar to what you will process
• Use the global flag: When you need all matches, use the g flag
• Anchor patterns: Use caret and dollar to limit search scope

Keyboard Shortcuts

Export Options

History and Recent Tests

The tool automatically saves your last 20 regex tests in browser localStorage. You can quickly reload any previous test by clicking on it in the history panel. This is useful for iterating on complex patterns or comparing different approaches.

Security and Privacy

Your privacy is important:

• 100% Client-Side: All regex processing happens in your browser
• No Server Communication: Nothing is sent to any server
• No Tracking: We do not track what patterns you test
• Local Storage Only: History is stored only in your browser
• No Third-Party Scripts: No analytics or tracking code

Common Errors and Solutions

Browser Compatibility

This tool works in all modern browsers including Chrome, Firefox, Safari, Edge, and Opera. The RegExp engine uses JavaScript native implementation, which is supported in all browsers released after 2015. All features including capture groups, flags, and replacements are fully supported.