Regex Tester – Free Developer Tool
Test regular expressions with live matching & highlighting. Free regex tester with pattern explanation, examples & instant validation.
The Online Regex Tester is a sophisticated developer utility designed to build, test, and debug Regular Expressions (RegEx) in real-time. Regular expressions are powerful sequences of characters that define search patterns, commonly used for string matching, data validation, and text transformation. While powerful, RegEx syntax can be notoriously difficult to get right without immediate feedback. Our tool solves this by providing instant visual highlighting of matches as you type.
Built with performance and security in mind, this tester supports various JavaScript regex flags like global (g), case-insensitive (i), and multiline (m). It includes a built-in safety check to detect 'Evil Regex' patterns that might cause Regular Expression Denial of Service (ReDoS) attacks. Whether you are validating email formats, scraping web data, or performing complex search-and-replace operations in your code, this tool offers the precision and privacy you need. All processing happens entirely within your browser, meaning your test data and patterns never leave your computer.
Features
- Test regex patterns
- Live matching
- Global, case-insensitive flags
- 100% client-side
- Free with no limits
How to Use
Enter your Regular Expression pattern in the top field (e.g., [a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,}).
Specify your search flags in the small input box; 'g' (global) is usually recommended to find all matches.
Paste the text you want to search through into the 'Test String' area.
Observe the real-time highlighting in the results card and click individual matches to copy them to your clipboard.
Frequently Asked Questions
What regex flavor is used?
JavaScript RegExp (ECMAScript). Flags: g (global), i (case-insensitive), m (multiline).
Is my text sent to a server?
No. Testing happens entirely in your browser. Your text never leaves your device.
Why does my pattern not match?
Check escaping (e.g., \d for digits), flags, and syntax. Use a regex reference for help.