Newtonsoft.Json by James Newton-King

<PackageReference Include="Newtonsoft.Json" Version="12.0.1" />

.NET API 553,384 bytes

 JsonExtensionDataAttribute

public class JsonExtensionDataAttribute : Attribute
Instructs the JsonSerializer to deserialize properties with no matching class member into the specified collection and write values during serialization.
public bool ReadData { get; set; }

Gets or sets a value that indicates whether to read extension data when deserializing the object.

public bool WriteData { get; set; }

Gets or sets a value that indicates whether to write extension data when serializing the object.

public JsonExtensionDataAttribute()

Initializes a new instance of the JsonExtensionDataAttribute class.