Regex Tester

A regular expression (regex) is a sequence of characters that defines a search pattern. It is used for pattern matching within strings — finding, replacing, or validating text. Regexes are supported in virtually every programming language.

g (global) finds all matches instead of stopping at the first. i (case-insensitive) ignores letter casing. m (multiline) makes ^ and $ match the start/end of each line. s (dotAll) makes the dot (.) match newline characters as well.

Common issues include forgetting the global flag (g) to find all matches, not escaping special characters like . or *, and incorrect character class syntax. This tool shows errors in real time to help you debug.

Capturing groups are parts of a regex enclosed in parentheses (). They capture the matched text for back-references or extraction. Non-capturing groups (?:...) group without capturing, which can improve performance.

Escape special regex characters with a backslash: \. matches a literal period, \* matches an asterisk, \[ matches a bracket, etc. Inside a character class [...], most special characters lose their meaning except ] \ ^ -.