Regex Tester & Validator

Matches any single character that is an uppercase letter, lowercase letter, digit, literal period, or underscore. This verbose alternation is equivalent to the compact character class [A-Za-z0-9._]. It's commonly used for validating usernames, identifiers, filenames, or other strings that allow alphanumeric characters plus dots and underscores. The global and multiline flags ensure every qualifying character is found across all lines of input.