Regex Tester

A regex is a pattern that describes a set of strings. It's used for searching, matching, and replacing text in programming and text editors.

g (global) finds all matches; i (case-insensitive) ignores case; m (multiline) makes ^ and $ match line boundaries; s (dotAll) makes . match newlines too.

Parentheses () in a regex create capture groups that extract specific parts of a match. For example, (\d+)-(\d+) captures two number groups.

* matches zero or more of the preceding element, while + matches one or more. So a* matches '' and 'aaa', but a+ requires at least one 'a'.

Yes. All regex processing happens in your browser. Nothing is sent to any server.

This tool uses JavaScript's built-in RegExp engine, which follows the ECMAScript specification. It supports features like Unicode property escapes (\p{L}), named capture groups (?<name>...), and lookbehind assertions. The syntax is compatible with most modern browsers and Node.js environments.

Use the 'm' (multiline) flag to make ^ and $ match the start and end of each line rather than the entire string. If you also need the dot (.) to match newline characters, enable the 's' (dotAll) flag. Combining both flags gives you full multiline pattern matching.

Yes. JavaScript supports positive lookahead (?=...), negative lookahead (?!...), positive lookbehind (?<=...), and negative lookbehind (?<!...). These zero-width assertions match a position without consuming characters, making them powerful for complex pattern matching like password validation or context-dependent replacements.