ASP.Net WebApi: Answer text/html requests with application/json

gistfile1.cs

public class JsonWithHtmlMediaTypeFormatter : JsonMediaTypeFormatter
    {
        public JsonWithHtmlMediaTypeFormatter()
        {
            SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
        }

        public override void SetDefaultContentHeaders(Type type, HttpContentHeaders headers, string mediaType)
        {
            base.SetDefaultContentHeaders(type, headers, mediaType);
            if(headers.ContentType.MediaType == "text/html")
                headers.ContentType = new MediaTypeHeaderValue("application/json");
        }
    }

You could rewrite the Header using a DelegatingHandler which evaluates whether you have a debug or release config active.
Or you could conditionally (based on active build config) add that Handler in your config.