An Accept header tells an HTTP server which media types a client can handle. During content negotiation, the server selects a supported format and identifies it with the response's Content-Type header. section 20.5
Ranking preferred formats
The header `application/json,text/xml;q=0.9,text/plain;q=0.6` accepts JSON, XML, and plain text. JSON has the highest preference because its default weighting is 1.0. section 20.5
ASP.NET Core web API controllers normally support JSON, text/plain, and text/html. Adding an XML output formatter makes a request with `text/xml` return XML instead of the default JSON. Without a usable Accept value, strings generally become text/plain and other models typically use the first suitable formatter. section 20.5.1 section 20.5.2
Browser requests are a notable exception: when Accept contains `*/*`, ASP.NET Core normally ignores content negotiation and uses its default formatter. Set `RespectBrowserAcceptHeader` to true when browser preferences must be honored. section 20.5.2
Listing 20.14 Customizing MVC to respect the browser’s Accept header in web APIs
WebApplicationBuilder builder = WebApplication.CreateBuilder(args); builder.Services.AddControllers(options => #1 { options.RespectBrowserAcceptHeader = true; #2 options.OutputFormatters.RemoveType<StringOutputFormatter>(); #3 }); #1 AddControllers has an overload that takes a lambda function. #2 False by default; several other properties are also available to be set. #3 Removes the output formatter that formats strings as text/plain
Use the MVC configuration listing to respect browser Accept headers and remove the string formatter that produces text/plain. section 20.5.2
