How to change default Web API 2 to JSON formatter?

Add this in your App_Start/WebApiConfig.cs:

config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));

I think Web API just uses the first formatter it can find in the Formatters collection. You can change the ordering with something like

GlobalConfiguration.Configuration.Formatters.Clear();
GlobalConfiguration.Configuration.Formatters.Add(new JsonMediaTypeFormatter());
GlobalConfiguration.Configuration.Formatters.Add(new XmlMediaTypeFormatter());

But it seems the JSON formatter should be the first one by default so you might want to check if you're already modifying this collection somewhere.

I think you should change as following. Global.asax:

/*For Indented formatting:*/       
 GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.Formatting = Newtonsoft.Json.Formatting.Indented;

    /*Response as default json format
     * example (http://localhost:9090/WebApp/api/user/)
     */
    GlobalConfiguration.Configuration.Formatters.XmlFormatter.SupportedMediaTypes.Clear();

    /*Response as json format depend on request type
     * http://localhost:9090/WebApp/api/user/?type=json
     */
    GlobalConfiguration.Configuration.Formatters.JsonFormatter.MediaTypeMappings.Add(
    new QueryStringMapping("type", "json", new MediaTypeHeaderValue("application/json")));

    /*Response as xml format depend on request type
     * http://localhost:9090/WebApp/api/user/?type=xml
     */
    GlobalConfiguration.Configuration.Formatters.XmlFormatter.MediaTypeMappings.Add(
    new QueryStringMapping("type", "xml", new MediaTypeHeaderValue("application/xml")));

Or just remove the XmlFormatter

var formatters = GlobalConfiguration.Configuration.Formatters;
formatters.Remove(formatters.XmlFormatter);

None of the above answers worked for me. The problem was that I was getting hold of the formatters from GlobalConfiguration and not the config object created with new HttpConfiguration() Here is the code that works for me :

public class WebApiConfig
{
    public static HttpConfiguration Register()
    {

        var config = new HttpConfiguration();
        // This next line could stay if you want xml formatting
        config.Formatters.Remove(config.Formatters.XmlFormatter);

        // This next commented out line was causing the problem
        //var jsonFormatter = GlobalConfiguration.Configuration.Formatters.JsonFormatter;

        // This next line was the solution
        var jsonFormatter = config.Formatters.JsonFormatter;
        jsonFormatter.UseDataContractJsonSerializer = false; // defaults to false, but no harm done
        jsonFormatter.SerializerSettings.DateFormatHandling = DateFormatHandling.IsoDateFormat;
        jsonFormatter.SerializerSettings.Formatting = Formatting.None;
        jsonFormatter.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();           

        // remaining irrelevant code commented out
        return config;
    }
}

FYI be careful of intercepting the text/html media type because this will also format the 404 responses from your server. And in my case, this led to a potential security issue because:

• malicious user browses to http://api.mysite.com/one/two?test=%3Cscript%3Ealert(%27hi%27)%3C/script%3E
• Web API returns the 404 object, which includes the URL. This is in JSON format because of the attribute above.
• Browser thinks the returned object is actually text/html, so it just renders the JSON object
• This causes the script tag embedded in the URL to execute. In my example URL above it is just an alert, but it could also be a window.location or anything sinister

config.EnableSystemDiagnosticsTracing();

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

// Adding formatter for Json   
config.Formatters.JsonFormatter.MediaTypeMappings.Add(new QueryStringMapping("type", "json", new MediaTypeHeaderValue("application/json")));

// Adding formatter for XML   
config.Formatters.XmlFormatter.MediaTypeMappings.Add(new QueryStringMapping("type", "xml", new MediaTypeHeaderValue("application/xml")));