Sometimes, the incoming data in JSON has some custom form that is not supported by the built-in Json.NET converters. In this article, as an educational example, we will implement a custom converter from the UNIX time format in milliseconds to the native .NET class DateTime.

Imagine a quite common client-server application where the server exposes REST methods and the client communicates using HTTP requests. Requests and responses are serialized in JSON format. There might be a problem if you try to send and receive a DTO that contains a collection of interfaces or abstract classes. I will talk about the usage of Web API and Newtonsoft Json.NET as its underlying serialization library.