// Set up application services public void ConfigureServices(IServiceCollection services) { services.AddMvc(options => { var formatFilter = new FormatFilterAttribute(); options.Filters.Add(formatFilter); var customFormatter = new CustomFormatter("application/custom"); options.OutputFormatters.Add(customFormatter); options.FormatterMappings.SetMediaTypeMappingForFormat( "custom", MediaTypeHeaderValue.Parse("application/custom")); }); }