How the Regex Tester Works

Our Regex Tester allows you to build, test, and debug regular expressions in your browser with real-time feedback.

Browser-Based Matching

This tool uses the built-in JavaScript RegExp engine to test your patterns against your input text:

1. Pattern Parsing: As you type your regular expression, we create a new RegExp object in JavaScript.
2. Flags Support: We support all standard JavaScript regex flags:
   • g (Global search)
   • i (Case-insensitive)
   • m (Multi-line)
   • s (DotAll)
   • u (Unicode)
   • y (Sticky)
3. Real-Time Feedback: We use exec() or matchAll() to find matches in your test string. We highlight these matches by splitting the text into spans with a specific CSS class.

Error Handling

If your regular expression is invalid, the JavaScript engine throws an error. We catch this error and display the specific reason (like "Unterminated group" or "Invalid escape character") to help you debug your pattern.

Privacy First

Testing regular expressions often involves sensitive data like logs, configuration files, or proprietary code.

• No Data Transmission: Both your regex pattern and your test text stay entirely in your browser.
• No Storage: We do not store, log, or transmit any part of your regex tests.
• Security: You can safely test regex patterns against sensitive data without worrying about it being sent to a server.

Verification

You can verify that this tool is 100% private by checking your browser's Network tab (F12). No requests to any server are made as you type your regex or your test text.