Enter a valid regex pattern to start testing
Regular expressions are powerful but notoriously difficult to write correctly on the first try. I built this interactive tester after spending too many hours debugging regex patterns in log parsers, input validators, and data extraction scripts. Instead of the traditional write-run-debug cycle, this tool shows matches in real-time as you type your pattern, with visual highlighting of captured groups. Whether you're validating email formats, parsing log files, extracting data from unstructured text, or cleaning up messy CSV exports, seeing immediate feedback dramatically speeds up development. The tool supports JavaScript regex syntax including lookaheads, lookbehinds, named groups, and Unicode property escapes. Includes common pattern examples (email, phone, URL, date formats) as starting templates, which has saved me countless Google searches.
How to Use
Enter your regular expression pattern in the pattern field (without surrounding slashes). Select flags: g (global—find all matches), i (case-insensitive), m (multiline—^ and $ match line breaks), s (dotall—dot matches newlines), u (Unicode). Paste or type test text in the test input area. Matches highlight automatically with different colors for capture groups. The tool shows: total match count, matched text with indexes, captured groups (numbered and named), and common errors (unmatched parentheses, invalid escapes). Use the examples dropdown to load common patterns as starting points. Test against multiple inputs to ensure your pattern handles edge cases—especially important for validation regex.
Limitations & Important Notes
This tool uses JavaScript regex engine (ECMA-262 standard). Patterns work in JS, but may need adjustments for other languages: Python uses different anchors for string boundaries, Java has varying support for advanced features, PCRE (PHP) has different Unicode handling. Complex patterns with excessive backtracking can cause performance issues or browser hangs—test with representative data volume. The tool is for testing and development—production validation should use tested libraries (validator.js, Joi, Yup) rather than custom regex when possible. Unicode handling: JavaScript regex supports Unicode categories only with u flag enabled. For very large texts over 1MB, performance degrades—use sampling. Regex alone cannot validate complex formats reliably: emails need domain validation, dates need calendar logic, HTML needs parsers not regex.