JsonModelBinder.cs

      public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
        {
            if (!IsJSONRequest(controllerContext))
            {
                return base.BindModel(controllerContext, bindingContext);
            }

            // get the JSON data that's been posted
            var request = controllerContext.HttpContext.Request;
            var jsonStringData = new StreamReader(request.InputStream).ReadToEnd();

            return new JavaScriptSerializer()
                .Deserialize(jsonStringData, bindingContext.ModelMetadata.ModelType);
        }

        static bool IsJSONRequest(ControllerContext controllerContext)
        {
            var contentType = controllerContext.HttpContext.Request.ContentType;
            return contentType.Contains("application/json");
        }
    }