System.text.json VS Newtonsoft.json

Sami C.
2 min readFeb 13, 2020

Microsoft shipped a new namespace called System.Text.Json with .NET Core 3.0. This one is integrated with .NET Core 3.0, so you no longer need to install a nuget package.

Why a new JSON serializer?

From what I’ve read I can basically tell you that Microsoft had trouble packaging Newtonsoft inside .NET Core 3.0. So they had to come up with a middle ground which ended up to be system.text.json. There’s also a speed improvement between the new one and the old one. Unfortunately, at a cost of some features that newtonsoft has.

Let’s take a look!

What is the new JSON serializer missing?

So I tried it on an existing code base and ended up with some interesting results:

The new json serializer does not support datamember attributes for naming


It can be a lot of effort to change all your DTO’s to support the new serializer.

Here is the original:


If you really want speed, then the new JSON serializer is most definitely not your best option. Utf8Json and JIL have been proved to be 2–4 times faster.

Referential loop handling

This sample sets ReferenceLoopHandling to Ignore so that looping values are excluded from serialization instead of throwing an exception.

string json = JsonConvert.SerializeObject(foo, Formatting.Indented, new JsonSerializerSettings
ReferenceLoopHandling = ReferenceLoopHandling.Ignore

This is not supported in the new JSON serializer, you’ll end up with exceptions. Although Jozkee made a comment that it should be available in the next version of .NET Core, which will be .NET 5.

Take a look at the comment:

More information can be found here:

Serializing dynamic types

The new serializer cannot serialize dynamic types.

dynamic p = JsonSerializer.Parse(json, typeof(ExpandoObject));

Github issue:


Let’s do a quick summary:

You want things to work and not worry about missing features?

Newtonsoft is the one to pick here!

Speed is your top priority?

Use something like Utf8Json.

Starting a new project?

I would use System.Text.Json and try to work around the missing features for now. I definitely believe there will be some improvements in the next version of .NET Core. Having the new serializer in your new projects will definitely give you a step ahead when upgrading to .NET 5.

Existing projects?

I advise you to stay on Newtonsoft until the missing features are actually added.

I hope you enjoyed the breakdown between the two.

Happy coding!