Regex Tester & Validator

Matches a non-negative integer per line: either a single digit (0-9) or a sequence whose first character is not a dot, zero, or hyphen followed by one or more digits. Intended to validate whole numbers without leading zeros, decimal points, or negative signs in multiline input. Note the first character class also allows letters, so strings like 'a5' pass; [1-9]\d+ would be stricter.