NewtonSoft.Json is an open source library. High-performance JSON framework for .NET also is an excellent JSON implementation widely adopted in the community, allows JSON serialization and deserialization. ASP.NET Web API has a dependency on this library. Author: James Newton-King.
There is a plug-in for Glimpse called Glipmse for Json.NET. Allows debug JSON on the server. Glimpse is a diagnostic tool for ASP.NET.