Json.NET is a popular high-performance JSON framework for .NET
Flexible JSON serializer for converting between .NET objects and JSON
LINQ to JSON for manually reading and writing JSON
High performance: faster than .NET's built-in JSON serializers
Write indented, easy-to-read JSON
Convert JSON to and from XML
Supports .NET 2, .NET 3.5, .NET 4, .NET 4.5, Silverlight, Windows Phone and Windows 8 Store
The JSON serializer in Json.NET is a good choice when the JSON you are reading or writing maps closely to a .NET class.
LINQ to JSON is good for situations where you are only interested in getting values from JSON, you don't have a class to serialize or deserialize to, or the JSON is radically different from your class and you need to manually read and write from your objects.
Json.NET was first released in June 2006. Since then Json.NET has been downloaded hundreds of thousands of times by developers from around the world. It is used in many major open source projects, including: Mono, an open source implementation of the .NET framework; RavenDB, a JSON based document database; ASP.NET SignalR, an async library for building real-time, multi-user interactive web applications; and ASP.NET Core, Microsoft's web app and service framework.