WebApi custom JsonConverter not called

I implemented a custom JsonConverter for Guids. If I declare it on the properties (of type Guid) of the class serialized like so ``` [JsonConverter(typeof(JsonGuidConverter))] ``` then it gets called and works fine. However, I'd like to use it "automatically", without needed the attributes, so I do this: ``` var formatters = GlobalConfiguration.Configuration.Formatters; var jsonFormatter = formatters.JsonFormatter; jsonFormatter.SerializerSettings.Converters.Add(new JsonGuidConverter()); ``` Unfortunately this results in my converter never getting called. I'm using WebApi 2.1 in a MVC 5.1 project. Any ideas? Edit: here is the converter code ``` public class JsonGuidConverter : JsonConverter { public override bool CanRead { get { // We only need the converter for writing Guids without dashes, for reading the default mechanism is fine return false; } } public override bool CanWrite { get { return true; } } public override bool CanConvert(Type objectType) { return objectType == typeof(Guid) || objectType == typeof(Guid?); } public override object ReadJson(JsonReader reader, Type objectType, object existingValue, Newtonsoft.Json.JsonSerializer serializer) { // We declared above CanRead false so the default serialization will be used throw new NotImplementedException(); } public override void WriteJson(JsonWriter writer, object value, Newtonsoft.Json.JsonSerializer serializer) { if (value == null || Guid.Empty.Equals(value)) { writer.WriteValue(string.Empty); } else { writer.WriteValue(((Guid)value).ToStringNoDashes()); } } } ``` Additional note, not even the CanRead/CanWrite properties and CanConvert method are called when trying to use it by adding it to the converters collection. Maybe it has something to do with how I return data from the webapi controller? ``` public async Task<IHttpActionResult> GetSettings() { ... return Json(something); } ```