What is System.Text.Json in C#: Overview and Usage

System.Text.Json is a built-in C# library for working with JSON data, allowing you to convert objects to JSON strings and JSON strings back to objects easily and efficiently. It provides fast, low-memory serialization and deserialization without needing external packages.

How It Works

Imagine you have a box of toys (your C# objects) and you want to send a list of those toys to a friend in a language they understand. System.Text.Json acts like a translator that turns your toys into a simple text list (JSON) and back again. It reads your objects and writes them as JSON strings, or reads JSON strings and rebuilds the objects.

This process is called serialization (object to JSON) and deserialization (JSON to object). The library uses efficient methods to do this quickly and with low memory use, making it great for apps that need to handle data fast or on limited devices.

Example

This example shows how to convert a simple C# object to a JSON string and then back to an 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 };

        // Convert object to JSON string
        string jsonString = JsonSerializer.Serialize(person);
        Console.WriteLine(jsonString);

        // Convert JSON string back to object
        Person person2 = JsonSerializer.Deserialize<Person>(jsonString);
        Console.WriteLine($"Name: {person2.Name}, Age: {person2.Age}");
    }
}

Output

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

When to Use

Use System.Text.Json whenever you need to work with JSON data in C#. It is ideal for web applications, APIs, and services that send or receive JSON. It helps when saving data to files, communicating between programs, or working with web data formats.

Because it is built into .NET Core 3.0 and later, it is a good choice for modern C# projects needing fast and simple JSON handling without extra dependencies.

Key Points

• Built-in JSON support in .NET Core 3.0+ and .NET 5+
• Fast and efficient serialization and deserialization
• Supports converting objects to JSON strings and back
• Good for web APIs, data storage, and communication
• Does not require external libraries like Newtonsoft.Json

Key Takeaways

System.Text.Json is the built-in C# library for JSON serialization and deserialization.

It converts C# objects to JSON strings and JSON strings back to objects efficiently.

Use it in modern .NET projects for fast, dependency-free JSON handling.

Ideal for web APIs, data exchange, and saving data in JSON format.