WCF (I think starting with version 3.51) has a nice "zero config" feature that integrates easily with IIS. All you have to do is

• create a JSON aware interface & service
• create a simple .SVC file in the IIS site.

You don't need to mess with funky .config files :-)

Example .SVC file:

<%@ ServiceHost
 Service="MyNamespace.MyService"
 Factory="System.ServiceModel.Activation.WebServiceHostFactory" %>

Example interface & service implementation, something like this:

public class MyService : IMyService
{
        public string Test(string text)
        {
            return text; // whatever
        }

}

[ServiceContractAttribute(Namespace="http://schemas.myservice.com")]
public interface IMyService
{
    [OperationContractAttribute]
    [WebInvokeAttribute(UriTemplate="Test", // change this accordingly
     ResponseFormat=WebMessageFormat.Json, // change this accordingly
     RequestFormat=WebMessageFormat.Json, // change this accordingly
     BodyStyle=Wrapped)]
    string Test(string text);
}

Here is an extra cool link about all this: WCF Web Services The Easy Way.