Sample JSON by C# class definition

I am looking for a code or lib which can create JSON by C# class definition. For example if I have an action (MVC or Web API):

[HttpGet]
[Route("Hosts")]
public void GetHosts(VendorSettings[] vendors)

And my classes defined as:

public class VendorSettings
{
    public string Vendor { get; set; }

    public int Id { get; set; }

    public StreamSettings Entitlements { get; set; }
}

public class StreamSettings
{
    public string Host { get; set; }

    public string Name { get; set; }
}

I want to see my documentation for this action as:

{
    Route: "Hosts/GetHosts",
    Parameters: 
    [
        {
            Name: "vendors",
            Type: "VendorSettings[]"
            /* I am looking for solution only for this part */
            Example:
            [
                {
                    Vendor: "",
                    Id: 0,
                    Entitlements: 
                    [
                        {
                            Host: "",
                            Name: ""
                        }
                    ]
                },
            ]
        },
    ],
}

I can handle all routing stuff, so my question is only about creating sample JSON by class defenition. I cannot create an instance of VendorSettings and use standard JSON serializer because it could be abstract or it could have no parameterless constructor. It is not a big deal to write it from scratch, but if someone already made same task I would love to reuse this code. Motivation is help page for selfhosted Web API.

Any links will be appreciated.