Regex Tester

Regular expressions (regex) are one of the most powerful — and most frustrating — tools in a developer's arsenal. A well-crafted regex can validate email addresses, extract phone numbers from unstructured text, parse log files, transform strings, and implement complex search-and-replace operations. But regex syntax is dense and unforgiving: a single misplaced character can change the entire meaning of a pattern, and debugging regex by trial-and-error in your application code is painfully slow.

Our Regex Tester provides a dedicated environment for building and debugging regular expressions in real-time. Type your regex pattern in the pattern field and your test string in the text area, and matches are highlighted instantly as you type. You can toggle flags (/g for global, /i for case-insensitive, /m for multiline) to see how they affect your results. Capture groups are extracted and displayed separately, showing you exactly what each parenthesized group captures from your test string.

The tool uses your browser's native JavaScript RegExp engine, which means the regex behavior you see is exactly what you will get in your JavaScript application code. This is important because regex implementations vary between languages — a pattern that works in Python's re module or Perl's regex engine may behave differently in JavaScript. By testing directly against the same engine your code will use, you eliminate the risk of engine-specific behavior differences.

Real-time highlighting is the key feature that makes this tool invaluable. Instead of writing a regex, running your code, checking the output, modifying the regex, and repeating, you see matches update instantly as you modify the pattern. This interactive feedback loop makes it dramatically faster to build and refine complex patterns, especially when working with edge cases and boundary conditions.