How do I get ASP.NET Web API to return JSON instead of XML using Chrome?

If you do this in the WebApiConfig you will get JSON by default, but it will still allow you to return XML if you pass text/xml as the request Accept header

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );

        var appXmlType = config.Formatters.XmlFormatter.SupportedMediaTypes.FirstOrDefault(t => t.MediaType == "application/xml");
        config.Formatters.XmlFormatter.SupportedMediaTypes.Remove(appXmlType);
    }
}

If you are not using the MVC project type and therefore did not have this class to begin with, see this answer for details on how to incorporate it.

I like Felipe Leusin's approach best - make sure browsers get JSON without compromising content negotiation from clients that actually want XML. The only missing piece for me was that the response headers still contained content-type: text/html. Why was that a problem? Because I use the JSON Formatter Chrome extension, which inspects content-type, and I don't get the pretty formatting I'm used to. I fixed that with a simple custom formatter that accepts text/html requests and returns application/json responses:

public class BrowserJsonFormatter : JsonMediaTypeFormatter
{
    public BrowserJsonFormatter() {
        this.SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
        this.SerializerSettings.Formatting = Formatting.Indented;
    }

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

Register like so:

config.Formatters.Add(new BrowserJsonFormatter());

MVC4 Quick Tip #3–Removing the XML Formatter from ASP.Net Web API

In Global.asax add the line:

GlobalConfiguration.Configuration.Formatters.XmlFormatter.SupportedMediaTypes.Clear();

like so:

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();

    RegisterGlobalFilters(GlobalFilters.Filters);
    RegisterRoutes(RouteTable.Routes);

    BundleTable.Bundles.RegisterTemplateBundles();
    GlobalConfiguration.Configuration.Formatters.XmlFormatter.SupportedMediaTypes.Clear();
}

In the WebApiConfig.cs, add to the end of the Register function:

// Remove the XML formatter
config.Formatters.Remove(config.Formatters.XmlFormatter);

source: http://www.asp.net/web-api/overview/formats-and-model-binding/json-and-xml-serialization

In the Global.asax I am using the code below. My url to get JSON is http://www.digantakumar.com/api/values?json=true

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();

    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
    RouteConfig.RegisterRoutes(RouteTable.Routes);
    BundleConfig.RegisterBundles(BundleTable.Bundles);

    GlobalConfiguration.Configuration.Formatters.JsonFormatter.MediaTypeMappings.Add(new  QueryStringMapping("json", "true", "application/json"));
}

Using RequestHeaderMapping works even better, because it also sets the Content-Type = application/json in the response header, which allows Firefox (with JSONView add-on) to format the response as JSON.

GlobalConfiguration.Configuration.Formatters.JsonFormatter.MediaTypeMappings.Add(new RequestHeaderMapping("Accept","text/html",StringComparison.InvariantCultureIgnoreCase,true,"application/json"));

Have a look at content negotiation in the WebAPI. These (Part 1 & Part 2) wonderfully detailed and thorough blog posts explain how it works.

In short, you are right, and just need to set the Accept or Content-Type request headers. Given your Action isn't coded to return a specific format, you can set Accept: application/json.

As the question is Chrome-specific, you can get the Postman extension which allows you to set the request content type.

One quick option is to use the MediaTypeMapping specialization. Here is an example of using QueryStringMapping in the Application_Start event:

GlobalConfiguration.Configuration.Formatters.JsonFormatter.MediaTypeMappings.Add(new QueryStringMapping("a", "b", "application/json"));

Now whenever the url contains the querystring ?a=b in this case, Json response will be shown in the browser.

I choose these codes since my default is json but if i want to use the XML format. I'll just append the xml=true.

GlobalConfiguration.Configuration.Formatters.XmlFormatter.MediaTypeMappings.Add(new QueryStringMapping("xml", "true", "application/xml"));
GlobalConfiguration.Configuration.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));

Thanks everyone!

Don't use your browser to test your API.

Instead, try to use an HTTP client that allows you to specify your request, such as CURL, or even Fiddler.

The problem with this issue is in the client, not in the API. The web API behaves correctly, according to the browser's request.

I used a global action filter to remove Accept: application/xml when the User-Agent header contains "Chrome":

internal class RemoveXmlForGoogleChromeFilter : IActionFilter
{
    public bool AllowMultiple
    {
        get { return false; }
    }

    public async Task<HttpResponseMessage> ExecuteActionFilterAsync(
        HttpActionContext actionContext,
        CancellationToken cancellationToken,
        Func<Task<HttpResponseMessage>> continuation)
    {
        var userAgent = actionContext.Request.Headers.UserAgent.ToString();
        if (userAgent.Contains("Chrome"))
        {
            var acceptHeaders = actionContext.Request.Headers.Accept;
            var header =
                acceptHeaders.SingleOrDefault(
                    x => x.MediaType.Contains("application/xml"));
            acceptHeaders.Remove(header);
        }

        return await continuation();
    }
}

Seems to work.

I found the Chrome app "Advanced REST Client" excellent to work with REST services. You can set the Content-Type to application/json among other things: Advanced REST client

From MSDN Building a Single Page Application with ASP.NET and AngularJS (about 41 mins in).

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        // ... possible routing etc.

        // Setup to return json and camelcase it!
        var formatter = GlobalConfiguration.Configuration.Formatters.JsonFormatter;
        formatter.SerializerSettings.ContractResolver =
            new Newtonsoft.Json.Serialization.CamelCasePropertyNamesContractResolver();
    }

It should be current, I tried it and it worked.

Some time has passed since this question was asked (and answered) but another option is to override the Accept header on the server during request processing using a MessageHandler as below:

public class ForceableContentTypeDelegationHandler : DelegatingHandler
{
    protected async override Task<HttpResponseMessage> SendAsync(
                HttpRequestMessage request,
                CancellationToken cancellationToken)
    {
        var someOtherCondition = false;
        var accHeader = request.Headers.GetValues("Accept").FirstOrDefault();
        if (someOtherCondition && accHeader.Contains("application/xml"))
        {
            request.Headers.Remove("Accept");
            request.Headers.Add("Accept", "application/json");
        }
        return await base.SendAsync(request, cancellationToken);
    }
}

Where someOtherCondition can be anything including browser type, etc. This would be for conditional cases where only sometimes do we want to override the default content negotiation. Otherwise as per other answers, you would simply remove an unnecessary formatter from the configuration.

You'll need to register it of course. You can either do this globally:

  public static void Register(HttpConfiguration config) {
      config.MessageHandlers.Add(new ForceableContentTypeDelegationHandler());
  }

or on a route by route basis:

config.Routes.MapHttpRoute(
   name: "SpecialContentRoute",
   routeTemplate: "api/someUrlThatNeedsSpecialTreatment/{id}",
   defaults: new { controller = "SpecialTreatment" id = RouteParameter.Optional },
   constraints: null,
   handler: new ForceableContentTypeDelegationHandler()
);

And since this is a message handler it will run on both the request and response ends of the pipeline much like an HttpModule. So you could easily acknowledge the override with a custom header:

public class ForceableContentTypeDelegationHandler : DelegatingHandler
{
    protected async override Task<HttpResponseMessage> SendAsync(
                HttpRequestMessage request,
                CancellationToken cancellationToken)
    {
        var wasForced = false;
        var someOtherCondition = false;
        var accHeader = request.Headers.GetValues("Accept").FirstOrDefault();
        if (someOtherCondition && accHeader.Contains("application/xml"))
        {
            request.Headers.Remove("Accept");
            request.Headers.Add("Accept", "application/json");
            wasForced = true;
        }

        var response =  await base.SendAsync(request, cancellationToken);
        if (wasForced){
          response.Headers.Add("X-ForcedContent", "We overrode your content prefs, sorry");
        }
        return response;
    }
}

Here is a solution similar to jayson.centeno's and other answers, but using the built-in extension from System.Net.Http.Formatting.

public static void Register(HttpConfiguration config)
{
    // add support for the 'format' query param
    // cref: http://blogs.msdn.com/b/hongyes/archive/2012/09/02/support-format-in-asp-net-web-api.aspx
    config.Formatters.JsonFormatter.AddQueryStringMapping("$format", "json", "application/json");
    config.Formatters.XmlFormatter.AddQueryStringMapping("$format", "xml", "application/xml");

    // ... additional configuration
 }

The solution was primarily geared toward supporting $format for OData in the early releases of WebApi, but it also applies to the non-OData implementation, and returns the Content-Type: application/json; charset=utf-8 header in the response.

It allows you to tack &$format=json or &$format=xml to the end of your uri when testing with a browser. It does not interfere with other expected behavior when using a non-browser client where you can set your own headers.

You just change the App_Start/WebApiConfig.cs like this:

public static void Register(HttpConfiguration config)
    {
        // Web API configuration and services

        // Web API routes
        config.MapHttpAttributeRoutes();
        //Below formatter is used for returning the Json result.
        var appXmlType = config.Formatters.XmlFormatter.SupportedMediaTypes.FirstOrDefault(t => t.MediaType == "application/xml");
        config.Formatters.XmlFormatter.SupportedMediaTypes.Remove(appXmlType);
        //Default route
        config.Routes.MapHttpRoute(
           name: "ApiControllerOnly",
           routeTemplate: "api/{controller}"
       );
    }

Its unclear to me why there is all of this complexity in the answer. Sure there are lots of ways you can do this, with query strings, and headers and options... but what I believe to be the best practice is simple. You request a plain URL (ex: http://yourstartup.com/api/cars) and in return you get json. You get json, with the proper response header:

Content-Type: application/json

In looking for an answer to this very same question, I found this thread, and had to keep going because this accepted answer doesn't work exactly. I did find an answer which I feel is just too simple not to be the best one:

Set the default WebAPI formatter

I'll add my tip here as well.

WebApiConfig.cs

namespace com.yourstartup
{
  using ...;
  using System.Net.Http.Formatting;
  ...
  config.Formatters.Clear(); //because there are defaults of XML..
  config.Formatters.Add(new JsonMediaTypeFormatter());
}

I do have a question of where the defaults (at least the ones I am seeing) come from. Are they .NET defaults, or perhaps created somewhere else (by someone else on my project). Anways, hope this helps.

Here is the easiest way that I have used in my applications. Add given below 3 lines of code in App_Start\\WebApiConfig.cs in Register function

    var formatters = GlobalConfiguration.Configuration.Formatters;

    formatters.Remove(formatters.XmlFormatter);

    config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/json"));

Asp.net web API will automatically serialize your returning object to JSON and as the application/json is added in the header so the browser or the receiver will understand that you are returning JSON result.