Regex Tester — Regular Expression Tester

A regular expression (regex or regexp) is a sequence of characters that defines a search pattern. It is used to find, match, validate, and replace text. For example, /^[\w.-]+@[\w.-]+\.\w{2,}$/ matches email addresses.

Common patterns: Email: /^[\w.-]+@[\w.-]+\.\w{2,}$/ | URL: /https?:\/\/[\w.-]+/ | Phone (US): /^\+?1?\d{10}$/ | IP Address: /\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/ | Date (YYYY-MM-DD): /\d{4}-\d{2}-\d{2}/

g (global) finds all matches instead of stopping at the first. i (case-insensitive) matches regardless of case. m (multiline) makes ^ and $ match start/end of each line. s (dotAll) makes . match newlines. The flags can be combined: /pattern/gi

* matches zero or more occurrences of the preceding element. + matches one or more occurrences. So /a*/ matches '', 'a', 'aa', 'aaa' etc., while /a+/ only matches 'a', 'aa', 'aaa' etc. (requires at least one).