egeek.dk - WCF return JSON, AJAX-enabled WCF Service in less than 3 minutes

Service1.svc.cs

[OperationContract]
public string HelloWorld(string personName)
{
    return (new HelloWorldWrapper
    {
        Response = string.Format("Hello, {0}", personName),
        Error = "",
        TimeExecuted = DateTime.Now.ToString(CultureInfo.InvariantCulture)
    }).ToJson();
}