Default Pipeline

By Default the DefaultJsonHandler is added to the beginning of the Pipeline, this deals with the required headers and serializing the JSON response content to a HttpResponse message, and tells RestClient that the response supports dynamic binding.

You can remove the DefaultJsonHandler from the Pipeline by setting UseDefaultHandlers to false:

var restClient = new RestClient("http://jsonplaceholder.typicode.com", 
                                new Config { UseDefaultHandlers = false });

When using IHttpClientFactory you can use the UseNoDefaultHandlers extension method when adding the RestClient to your .NET Core DI container (usually in Startup.cs):

services
   .AddRestClient("http://jsonplaceholder.typicode.com")
   .UseNoDefaultHandlers();