Regex Tester
Test and debug regular expressions in real-time with match highlighting.
How to Use Regex Tester
- Enter your regular expression pattern in the regex input field.
- Select the appropriate flags (global, case insensitive, multiline, etc.).
- Type or paste your test string in the textarea below.
- View highlighted matches instantly, with detailed match information including capture groups and positions.
About Regex Tester
The Regex Tester is a free online tool for testing and debugging regular expressions in real-time. As you type your pattern and test string, matches are highlighted instantly with detailed information about each match including capture groups and character positions. Whether you're validating email formats, parsing log files, or extracting data from text, this tool helps you build and verify regex patterns quickly. Includes a built-in cheat sheet for quick reference.
Frequently Asked Questions
What regex flavor does this tool use?
This tool uses JavaScript's native RegExp engine, which supports ECMAScript regex syntax including lookahead, lookbehind, named groups, and Unicode properties.
Does my data leave my browser?
No. All regex processing happens entirely in your browser using JavaScript. No data is sent to any server.
What do the regex flags mean?
g (global) finds all matches instead of stopping at the first. i (case insensitive) ignores letter casing. m (multiline) makes ^ and $ match line starts/ends. s (dotAll) makes . match newlines. u (unicode) enables full Unicode matching.
Can I test regex for other languages like Python or PHP?
This tool uses JavaScript regex syntax, which is very similar to most languages. However, some advanced features like possessive quantifiers or recursive patterns (available in PCRE/PHP) are not supported in JavaScript.
Is there a limit on the test string size?
There's no hard limit, but very large strings (100,000+ characters) may slow down real-time highlighting. For best performance, test with representative samples.
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