Creating a JSON object in ASP.Net

I would use Json.Net to create the JSON payloads for sure (Afterall, Microsoft does for Web Api).

Nuget Package Source:

Install-Package Newtonsoft.Json

Here is an example. If you want to call a REST api that returns a product when you make a GET call then you might do something like this.

public static class Main
{
    string url = "https://TheDomainYouWantToContact.com/products/1";
    HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
    request.Method = "GET";
    request.ContentType = "application/json";
    request.Accept = "application/json";
    var httpResponse = (HttpWebResponse)request.GetResponse();

    var dataStream = httpResponse.GetResponseStream();
    var reader = new StreamReader(dataStream);
    var responseFromServer = reader.ReadToEnd();
    reader.Close();
    dataStream.Close();

    // This is the code that turns the JSON string into the Product object.
    Product productFromServer = JsonConvert.Deserialize<Product>(responseFromServer);
    Console.Writeline(productFromServer.Id);
}

// This is the class that represents the JSON that you want to post to the service.
public class Product
{
    public string Id { get; set; }
    public decimal Cost { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
}

The exact same method can be used for POST and PUT as well.

You can use 3rd party assemblies to make this super easy too. We are the authors of DynamicApis.Api

Install-Package DynamicApis.Api

The code to make the same request using this client would be:

public static class Main
{
    RestClient client = new RestClient();
    string url = "https://YourDomain.com/products/1";
    var productFromServer = client.Get<Product>(url);
    Console.Writeline(productFromServer.Id);
}

you should use NewtonSoft.Json if you need to serialize objects as json

You shouldn't have to do anything special to send back Json data. The default output formatter is already Json, and if your Startup.cs file is somewhat normal, you should have a line similar to this:

services.AddMvc();

By default, this already contains the Json formatter, and your controller should autonegotiate the return type based on what the browser asked. So a controller like the following should work (taken from this Github issue, which contains some information on why/how this work):

public class ValuesController : ApiController
{
    public SomeClass Get()
    {
        return new SomeClass();
    }

    public SomeClass Post([FromBody] SomeClass x)
    {
        return x;
    }
}