System.Text.Json vs Newtonsoft.Json in C#: Key Differences and Usage

In C#, System.Text.Json is a modern, high-performance JSON library built into .NET Core 3.0+ focusing on speed and low memory use, while Newtonsoft.Json (Json.NET) is a mature, feature-rich library with broader compatibility and more customization options. Choose System.Text.Json for better performance and built-in support, and Newtonsoft.Json when you need advanced features or compatibility with older .NET versions.

Quick Comparison

This table summarizes the key differences between System.Text.Json and Newtonsoft.Json.

Feature	System.Text.Json	Newtonsoft.Json
Introduced	.NET Core 3.0 (2019)	2006 (third-party library)
Performance	Faster and uses less memory	Slower but flexible
Customization	Limited converters and options	Extensive converters and settings
Compatibility	.NET Core 3.0+, .NET 5+	.NET Framework, .NET Core, .NET 5+
Features	Basic JSON support, no LINQ to JSON	Full JSON support, LINQ to JSON, schema validation
Community & Support	Official Microsoft support	Large community, many extensions

Key Differences

System.Text.Json is designed for speed and low memory use, making it ideal for high-performance applications. It is built into the .NET runtime starting with .NET Core 3.0, so no extra packages are needed. However, it has fewer features and less flexibility compared to Newtonsoft.Json.

Newtonsoft.Json, also known as Json.NET, has been the go-to JSON library for .NET developers for many years. It supports advanced features like LINQ to JSON, extensive customization of serialization, and schema validation. It works with older .NET Framework versions and has a large ecosystem of extensions.

While System.Text.Json is catching up with new features, it currently lacks some capabilities like full polymorphic serialization and advanced date handling. Developers often choose Newtonsoft.Json when they need these advanced features or compatibility with legacy projects.

Code Comparison

Here is how to serialize and deserialize a simple object using System.Text.Json.

csharp

using System;
using System.Text.Json;

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
}

public class Program
{
    public static void Main()
    {
        var person = new Person { Name = "Alice", Age = 30 };

        // Serialize to JSON
        string json = JsonSerializer.Serialize(person);
        Console.WriteLine(json);

        // Deserialize from JSON
        var deserialized = JsonSerializer.Deserialize<Person>(json);
        Console.WriteLine($"Name: {deserialized.Name}, Age: {deserialized.Age}");
    }
}

Output

{"Name":"Alice","Age":30}
Name: Alice, Age: 30

Newtonsoft.Json Equivalent

Here is the equivalent code using Newtonsoft.Json (Json.NET) for the same task.

csharp

using System;
using Newtonsoft.Json;

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
}

public class Program
{
    public static void Main()
    {
        var person = new Person { Name = "Alice", Age = 30 };

        // Serialize to JSON
        string json = JsonConvert.SerializeObject(person);
        Console.WriteLine(json);

        // Deserialize from JSON
        var deserialized = JsonConvert.DeserializeObject<Person>(json);
        Console.WriteLine($"Name: {deserialized.Name}, Age: {deserialized.Age}");
    }
}

Output

{"Name":"Alice","Age":30}
Name: Alice, Age: 30

When to Use Which

Choose System.Text.Json when:

• You want the best performance and low memory use.
• You are targeting .NET Core 3.0 or later and want built-in support.
• Your JSON needs are simple without advanced customization.

Choose Newtonsoft.Json when:

• You need advanced features like LINQ to JSON, custom converters, or schema validation.
• You are working with older .NET Framework versions.
• Your project requires extensive customization or third-party extensions.

In summary, System.Text.Json is great for modern, fast applications, while Newtonsoft.Json remains the best choice for complex scenarios and legacy support.

Key Takeaways

System.Text.Json is faster and built into modern .NET versions.

Newtonsoft.Json offers more features and better customization.

Use System.Text.Json for simple, high-performance needs.

Use Newtonsoft.Json for advanced JSON handling or legacy projects.

Both libraries produce similar JSON output for basic serialization tasks.