public static function isJson (string $string) : bool
    {
        if (is_numeric($string) || $string === 'true' || $string === 'false' || $string === 'null' || empty($string)) :
            return false;
        endif;

        // try to decode string
        json_decode($string);

        // check if error occured
        return json_last_error() === JSON_ERROR_NONE;
    }