ASP.NET: Then vs Now — JSON Serialization Performance

Coder Thiyagarajan
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Article

Back in the day, we mostly used Newtonsoft.Json.
It was flexible, but not the fastest.

Now in ASP.NET 8, the built-in System.Text.Json is 🔥 optimized for speed & memory.

Then (Newtonsoft.Json)

  
    var json = JsonConvert.SerializeObject(myObject);

Now (System.Text.Json)

  
    var json = JsonSerializer.Serialize(myObject);

🚀 Benchmarks

50–70% faster than Newtonsoft

Much lower memory allocations

Built-in for all ASP.NET APIs (no extra package)

✅ For most apps, System.Text.Json is the best choice.
✅ Use Newtonsoft.Json only if you need advanced features (e.g., polymorphic serialization).

Pro tip: In .NET 8, System.Text.Json now supports required properties, polymorphism, and contract customization — so even fewer reasons to use Newtonsoft.

👉 Question: Are you still using Newtonsoft.Json in your ASP.NET projects, or have you switched completely?