How to deserialize a part of JSON as a string keeping everything inside as is including the formatting? Or how to merge JSONs together into one having them provided as strings? The article shows an implement of a custom converter for the System.Text.Json that does described things, and provides additional cases when such converter might be useful.

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.