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Home Forums How do you read and write JSON data to a file in C#? – MindStick
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1 Answers

Utpal Vishwas
Utpal Vishwas 20 May 2025
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To read and write JSON data to a file in C#, you typically use the System.Text.Json namespace (built-in since .NET Core 3.0+). You can also use Newtonsoft.Json if you prefer, but here's how to do it using the built-in approach:

1. Define a C# Model

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

2. Write JSON to a File

using System.Text.Json;
using System.IO;
var person = new Person { Name = "Alice", Age = 30 };
string jsonString = JsonSerializer.Serialize(person, new JsonSerializerOptions { WriteIndented = true });
File.WriteAllText("person.json", jsonString);  // Writes to file

3. Read JSON from a File

string jsonFromFile = File.ReadAllText("person.json");
Person personFromFile = JsonSerializer.Deserialize<Person>(jsonFromFile);
Console.WriteLine($"{personFromFile.Name} is {personFromFile.Age} years old.");

Notes:

  1. JsonSerializer.Serialize(object) converts a C# object to JSON.
  2. JsonSerializer.Deserialize<T>(json) parses JSON into a C# object.
  3. The optional WriteIndented = true makes the JSON more readable.

Using Newtonsoft.Json (if preferred):

dotnet add package Newtonsoft.Json

Example:

using Newtonsoft.Json;

var person = new Person { Name = "Bob", Age = 25 };
File.WriteAllText("person.json", JsonConvert.SerializeObject(person, Formatting.Indented));

string json = File.ReadAllText("person.json");
Person loaded = JsonConvert.DeserializeObject<Person>(json);

Summary

Task Built-in API Newtonsoft.Json Equivalent
Serialize to file JsonSerializer.Serialize JsonConvert.SerializeObject
Deserialize from file JsonSerializer.Deserialize JsonConvert.DeserializeObject
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