ServiceStack supports the following formats:
- JSON
 - XML
 - CSV
 - JSONL
 - JSV (hybrid CSV-style escaping + JSON format that is optimized for both size and speed)
 - SOAP 1.1/1.2 (requires ASP.NET Framework)
 - Message Pack
 - Protocol Buffers
 - HTML
- #Script Pages (Simple, clean, fast alternative to Razor)
 - Razor (Microsoft's Razor View Engine)
 - Markdown Razor (Razor-inspired syntax combined with markdown)
 - HTML5 Report (Human-friendly HTML auto-layout to quickly visualize data returned by services)
 
 
.NET Service Clients​
The different Content Types can be easily consumed using ServiceStack's Typed Generic Service Clients.
HTTP API Formats​
ServiceStack Services supports a number of Content Negotiation options where you can define which
format should be returned by adding a .{format} extension to your /route.{format}. Built-in Formats include:
.json.xml.jsv.csv.html
Example: http://web.web-templates.io/hello/World.json
Or by appending ?format={format} to the end of the URL:
?format=json?format=xml?format=jsv?format=csv?format=html
Example: http://web.web-templates.io/hello/World?format=json
Alternatively ServiceStack also recognizes which format should be used with the Accept http header:
Accept: application/jsonAccept: application/xml
Default Content-Type​
The recommended way to request a specific content type is to add it to the Accept HTTP Request Header, e.g:
Accept: application/json
Alternatively you can specify to use a specific Content-Type as the default Content Type in your AppHost with:
SetConfig(new HostConfig {
     DefaultContentType = MimeTypes.Json 
});
Sometimes when calling web services from a web browser they'll ask for Accept: text/html and not JSON which by contract ServiceStack obliges by returning back HTML if it is enabled.
To ensure JSON is always returned you can disable the HTML support with:
SetConfig(new HostConfig {
    EnableFeatures = Feature.All.Remove(Feature.Html),
});
Pre-defined Routes​
/[xml|json|html|jsv|csv]/[reply|oneway]/[servicename]
Examples:
- /json/reply/Hello (JSON)
 - /xml/oneway/SendEmail (XML)
 
Forcing a Content Type​
Whilst ServiceStack Services are typically available on any endpoint and format, there are times when you only want adhoc Services available in a particular format, for instance you may only want the View Models for your dynamic Web Views available in HTML. This can now be easily enabled with the new [HtmlOnly] Request Filter Attribute, e.g:
[HtmlOnly]
public class HtmlServices : Service
{
    public object Any(MyRequest request) => new MyViewModel { .. };
}
This feature is also available for other built-in Content Types: [JsonOnly], [XmlOnly], [JsvOnly] and [CsvOnly].
Registering a Custom Format​
Registering a custom format is done by registering the Format's Content-Type with to your AppHost's ContentTypes API, e.g:
//Register the 'text/csv' content-type format
//Note: Format is inferred from the last part of the content-type, e.g. 'csv'
public class CsvFormat : IPlugin
{
    public void Register(IAppHost appHost)
    {
        appHost.ContentTypes.Register(MimeTypes.Csv,
            SerializeToStream, 
            CsvSerializer.DeserializeFromStream);
        //ResponseFilter to add 'Content-Disposition' header for browsers to open in Spreadsheet
        appHost.GlobalResponseFilters.Add((req, res, dto) => {
            if (req.ResponseContentType == MimeTypes.Csv) {
                var fileName = req.OperationName + ".csv";
                res.AddHeader(HttpHeaders.ContentDisposition, 
                    $"attachment;{HttpExt.GetDispositionFileName(fileName)}");
            }
        });
    }
    void SerializeToStream(IRequest req, object request, Stream stream) =>
        CsvSerializer.SerializeToStream(request, stream);
}
We recommend encapsulating Custom Formats registrations into a Plugin as done with the built-in CsvFormat which is added by default:
Plugins.Add(new CsvFormat()); //added by default
Which makes it easy to register, detect and remove. E.g. to remove built-in support for CSV you can just remove it from the Plugins collection:
Plugins.RemoveAll(x => x is CsvFormat);
XmlSerializerFormat Plugin​
The XmlSerializerFormat plugin changes ServiceStack to serialize XML with .NET XmlSerializer instead of .NET XML
DataContractSerializer:
Plugins.Add(new XmlSerializerFormat());
The implementation provides a typical example of how to register or override different Content-Types in ServiceStack:
public class XmlSerializerFormat : IPlugin
{
    public static void Serialize(IRequest req, object response, Stream stream)
    {
        var serializer = new XmlSerializer(response.GetType());
        serializer.Serialize(stream, response);
    }
    public static object Deserialize(Type type, Stream stream)
    {
        var serializer = new XmlSerializer(type.GetType());
        var obj = (Type) serializer.Deserialize(stream);
        return obj;
    }
    public void Register(IAppHost appHost)
    {
        appHost.ContentTypes.Register(MimeTypes.Xml, Serialize, Deserialize);
    }
}
SOAP Endpoint​
Consume ServiceStack Services via SOAP using WCF Add Service Reference or ServiceStack generic SOAP Clients.
MQ Endpoint​
Consume ServiceStack Services via Message Queue.