Free Online Regex Tester
Test & debug regular expressions in real time
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About this tool
Test and debug regular expressions in real time with this free online regex tester. Type your pattern, set flags (global, case-insensitive, multiline, dotAll, Unicode), and see matches highlighted instantly in your test string. The tool shows every match with its position index and captured groups, making it easy to verify that your regex does exactly what you expect. Matches are color-highlighted directly in the test string so you can visually confirm coverage. Invalid patterns show clear error messages from the JavaScript regex engine so you can fix syntax issues immediately. The tester uses JavaScript's native RegExp — what you see here is exactly what your code will produce. Whether you are writing a validation pattern for email addresses, parsing log files, extracting data from text, or learning regex syntax, this tool gives you instant visual feedback. All processing runs entirely in your browser with no data sent to any server.
Frequently Asked Questions
This tester uses JavaScript's built-in RegExp engine, which implements the ECMAScript regex specification. This means the patterns you test here will work identically in JavaScript, TypeScript, and Node.js code. Other languages (Python, Java, Ruby) have slightly different regex flavors — some features like lookbehinds or Unicode property escapes may behave differently.
g (global) finds all matches instead of stopping at the first. i (case-insensitive) matches regardless of letter case. m (multiline) makes ^ and $ match the start/end of each line instead of the whole string. s (dotAll) makes the . character match newlines too. u (unicode) enables full Unicode matching and makes quantifiers work correctly with astral characters like emoji.
Common issues: forgetting to enable the g flag (only finds the first match), not escaping special characters like . or * (they have special meaning in regex), using ^ or $ without the m flag when testing multiline input, or a typo in the pattern. Check the error message below the pattern input — it will tell you if your syntax is invalid.
Parentheses () in a regex create capturing groups that extract specific parts of a match. For example, the pattern (\d{3})-(\d{4}) matching '555-1234' captures '555' as group 1 and '1234' as group 2. Named groups use (?<name>...) syntax. This tool shows all captured groups in a separate table below the matches.
No. All regex matching happens entirely in your browser using JavaScript's native RegExp engine. No patterns or test strings are transmitted, stored, or logged. Your data stays completely private on your device.
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