JsonConverters

JsonConverters are components that customize how objects are serialized to and deserialized from JSON. They are used by JSON libraries to extend default serialization behavior and to handle types that the built-in rules cannot process reliably. Notable implementations appear in Newtonsoft.Json as JsonConverter and in System.Text.Json as JsonConverter or JsonConverter<T>.

A converter provides logic to write a type’s JSON representation and to read JSON back into an object. They enable support for non-standard formats, strict or custom representations, and complex or polymorphic types. Converters can be applied at the property level with attributes, at the type level, or registered globally in serializer options or settings.

Common use cases include formatting dates and times in a specific string form, serializing enums as strings or numbers, handling polymorphic hierarchies with type discriminators, and converting non-JSON-native types such as GUID, TimeSpan, or custom domain types.

In practice, a converter is created by subclassing the appropriate abstract class and implementing the read and write methods. When registered, the serializer delegates to the converter for matching types, ensuring consistent and centralized customization. Performance considerations include keeping converters lightweight and avoiding unnecessary allocations. Maintenance concerns involve keeping converters compatible with library updates and ensuring consistent behavior across versions.

See also: JSON serialization, Newtonsoft.Json, System.Text.Json, JsonSerializer, JsonConverter.