server side validation

hi all,
      i have done the client side validation in tooltip ajax validation, the same i want generate server side validation in tooltip.. actually i php they call
echo '{"jsonValidateReturn":'.json_encode($arrayToJs).'}';
to display the user present or not..
how i call the JSON_encode in .net .
i used following code..


protected void Page_Load(object sender, EventArgs e)
    {
       

        string name = Request.Form[0];
        string value1 = Request.Form[1];
        string value2 = Request.Form[2];

        string val1 = "true";
        string val2 = "false";

   ...