Regex Tester

Free Online Regex Tester & Debugger

Test and debug regular expressions in real-time. See matches highlighted, capture groups, and match positions. Supports JavaScript regex syntax with global, case-insensitive, multiline, and dotAll flags.

Enter your regular expression pattern in the regex input field at the top, then paste or type your test text in the main editor below. Matches highlight instantly in the text, with different colors for each capture group. The match count, specific matched strings, and capture group contents display in the sidebar. Toggle flags like global (g), case-insensitive (i), multiline (m), and dotAll (s) using the checkboxes. The tool uses JavaScript regex engine syntax, so patterns work identically to code you write in JS. All testing happens live in your browser.

Developers validate regex patterns for form validation rules before implementing them in production code, testing against various input edge cases. Data engineers build patterns to extract structured information from log files or unformatted text dumps. Backend programmers debug route matching expressions for frameworks like Express or Rails that use regex for URL patterns. Security analysts test input sanitization patterns to ensure they catch all variations of potentially malicious strings without false positives.

Build your pattern incrementally, testing after adding each component rather than writing the entire regex at once and debugging failures. Use capture groups with parentheses to extract specific portions of matches rather than just finding them. When working with user input, test edge cases like empty strings, strings with only whitespace, and extremely long inputs that might cause catastrophic backtracking. Use non-capturing groups (?:...) instead of capturing groups when you don't need to extract the content, improving performance on large text. If your pattern seems too complex, consider whether multiple simpler regex passes might be more maintainable than one intricate expression.

All processing happens directly in your browser. Your files never leave your device — no server uploads, no cloud storage, no data retention. The tool works offline once loaded, requires no registration, and is completely free with no usage limits.