// the find
JamesNK/Newtonsoft.Json
Json.NET is a popular high-performance JSON framework for .NET
Newtonsoft.Json is the JSON library that dominated .NET for over a decade before System.Text.Json shipped in .NET Core 3. It's still the right choice when you need LINQ-to-JSON, deep serialization customization via contract resolvers, or you're maintaining a legacy codebase that can't absorb a migration.
The contract resolver system is genuinely powerful — you can reshape serialization behavior at runtime in ways System.Text.Json still can't match without source generators. LINQ-to-JSON (JObject/JArray/JToken) is a practical API for working with unknown or dynamic JSON structures. The test suite and fuzzing setup are thorough, which matters for a library parsing untrusted input. Thirteen years of edge cases means the weird stuff — circular references, polymorphic type handling, XML interop — actually works.
It allocates heavily by design; if you're on a hot path and care about allocations, System.Text.Json with Utf8JsonReader will beat it by a wide margin. The library is effectively in maintenance mode — James NK has said as much publicly, so new .NET features (required members, init-only properties, discriminated unions) get partial or no support. TypeNameHandling with untrusted input is a well-documented deserialization gadget vector; the docs warn about it, but people still ship it wrong. If you're starting a new .NET 8+ project, you're picking this for compatibility reasons, not because it's the better tool.