JSON to C# Class

What is JSON to C# Conversion?

JSON to C# conversion is the process of generating strongly-typed C# class definitions from JSON data. When a .NET application receives JSON from an API, configuration file, or message queue, it needs C# classes to deserialize that data into objects. Writing these classes by hand is tedious and error-prone, especially when the JSON contains nested objects, arrays, and mixed types.

A JSON to C# class generator inspects the structure and values in your JSON, infers the appropriate C# type for each field, and produces class definitions with property accessors and serialization attributes. The output follows .NET naming conventions: PascalCase property names, JsonPropertyName attributes for mapping to the original camelCase or snake_case JSON keys, and correct use of List'<'T'>' for arrays.

This conversion is especially common in ASP.NET Core web APIs, Azure Functions, and any .NET service that consumes external JSON data. Rather than using dynamic or Dictionary'<'string, object'>', typed classes give you compile-time safety, IntelliSense support, and protection against field name typos that would otherwise only surface at runtime. Paste your JSON into this tool and get ready-to-use C# classes instantly.

Why Use a JSON to C# Generator?

Manually writing C# model classes from JSON samples takes time and introduces human error. A generator handles the repetitive parts so you can focus on business logic.

JSON to C# Use Cases

JSON to C# Type Mapping Reference

Each JSON value type maps to a specific C# type. The generator analyzes actual values to pick the most precise type. For example, a JSON number with no decimal point becomes int, while 3.14 becomes double. Null values produce object? (nullable reference type) since the actual type cannot be inferred from null alone.

System.Text.Json vs Newtonsoft.Json

.NET has two major JSON serialization libraries. The generated classes from this tool use System.Text.Json attributes (JsonPropertyName), which is the built-in option since .NET Core 3.0. If your project uses Newtonsoft.Json, you can swap the attributes.

Code Examples

These examples show how to define and use C# classes generated from JSON, using both major serialization libraries, plus how to automate generation from the command line.

using System.Text.Json;

var json = """{"id": 1, "name": "Alice", "active": true}""";
var user = JsonSerializer.Deserialize<User>(json);
Console.WriteLine(user.Name); // → "Alice"

public class User
{
    [JsonPropertyName("id")]
    public int Id { get; set; }

    [JsonPropertyName("name")]
    public string Name { get; set; }

    [JsonPropertyName("active")]
    public bool Active { get; set; }
}

using Newtonsoft.Json;

var json = @"{""id"": 1, ""name"": ""Alice"", ""scores"": [98, 85]}";
var user = JsonConvert.DeserializeObject<User>(json);
Console.WriteLine(user.Scores[0]); // → 98

public class User
{
    [JsonProperty("id")]
    public int Id { get; set; }

    [JsonProperty("name")]
    public string Name { get; set; }

    [JsonProperty("scores")]
    public List<int> Scores { get; set; }
}

// Install: npm install -g quicktype
// Generate C# classes from JSON:
// quicktype --lang csharp --src data.json --out Models.cs

// From stdin:
// echo '{"id": 1, "name": "Alice"}' | quicktype --lang csharp

// Output:
// public class Root
// {
//     [JsonPropertyName("id")]
//     public int Id { get; set; }
//
//     [JsonPropertyName("name")]
//     public string Name { get; set; }
// }

import json

def json_to_csharp(data: dict, class_name: str = "Root") -> str:
    lines = [f"public class {class_name}", "{"]
    type_map = {str: "string", int: "int", float: "double", bool: "bool"}

    for key, value in data.items():
        cs_type = type_map.get(type(value), "object")
        prop = key[0].upper() + key[1:]  # PascalCase
        lines.append(f'    [JsonPropertyName("{key}")]')
        lines.append(f'    public {cs_type} {prop} {{ get; set; }}')
        lines.append('')
    lines.append("}")
    return "\n".join(lines)

data = json.loads('{"id": 1, "name": "Alice", "active": true}')
print(json_to_csharp(data))

Frequently Asked Questions