Generate C# Classes
from JSON

C# class definitions in four steps

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Common questions answered

Converting JSON to C# classes

C# uses classes or records for JSON data. System.Text.Json (modern) or Newtonsoft.Json deserialize JSON into these types. This tool generates complete C# class definitions with PascalCase properties, .NET types (string, int, double, bool), and [JsonPropertyName] attributes for proper mapping.

The converter follows .NET conventions: PascalCase class and property names, { get; set; } auto-properties, separate classes for nested objects, and List<T> for arrays. When JSON keys are camelCase, it adds [JsonPropertyName] attributes. The output targets C# 10+ with nullable reference types.

{
  "userName": "Alice",
  "age": 30,
  "roles": ["admin"],
  "address": {
    "city": "Portland"
  }
}

public class Root
{
    [JsonPropertyName("userName")]
    public string UserName { get; set; }
    [JsonPropertyName("age")]
    public int Age { get; set; }
    [JsonPropertyName("roles")]
    public List<string> Roles { get; set; }
    [JsonPropertyName("address")]
    public Address Address { get; set; }
}

public class Address
{
    [JsonPropertyName("city")]
    public string City { get; set; }
}

Get the most out of this tool

• Use System.Text.Json (built into .NET) instead of Newtonsoft.Json for new projects — it is faster with no external dependency.
• [JsonPropertyName] maps JSON camelCase keys to C# PascalCase — generated automatically by this tool.
• Review generated classes for nullable types (string?) — add validation for required fields in your business logic.

C# classes for JSON with System.Text.Json and Newtonsoft

C# and the .NET ecosystem have two major JSON libraries: System.Text.Json (built into .NET Core 3.0+ and .NET 5+) and Newtonsoft.Json (Json.NET, the long-standing community standard). Both serialize and deserialize JSON to C# classes, but with different attribute names and behavior. The converter generates C# POCO (Plain Old CLR Object) classes with appropriate annotations for both libraries, giving you a head start on JSON integration in any .NET project.

JSON types map to C# types as follows: JSON strings become string (nullable reference type in C# 8+ with nullable context enabled). JSON integers become int or long. JSON floating-point numbers become double. JSON booleans become bool. JSON null maps to nullable types — string? or int? in C# 8+ with nullable reference types enabled, or just string for older code. JSON arrays become List<T> or T[]. Nested JSON objects become separate C# class definitions.

Property naming conventions differ between JSON (camelCase or snake_case) and C# (PascalCase). The converter generates PascalCase property names (as per C# conventions) and adds [JsonPropertyName("jsonKey")] (System.Text.Json) or [JsonProperty("jsonKey")] (Newtonsoft.Json) attributes to handle the name mapping. Alternatively, you can configure the serializer globally with JsonSerializerOptions using camelCase naming policy, eliminating the need for per-property attributes.

ASP.NET Core Web API uses System.Text.Json by default in .NET 6+. Controller actions returning objects are automatically serialized to JSON responses. [FromBody] parameters are automatically deserialized from the request body. The generated C# classes work directly as controller action parameter types and return types — no additional configuration is needed for basic JSON API development in ASP.NET Core.

Nullable reference types, introduced in C# 8 and enabled by default in .NET 6+ projects, add compile-time null safety similar to TypeScript. String becomes non-nullable by default — to allow null, you must write string?. When a JSON field might be absent or null, the converter marks its C# type as nullable. If your project has nullable reference types enabled, these annotations prevent null reference exceptions that would otherwise only surface at runtime.

Records, introduced in C# 9, provide an immutable alternative to regular classes for data transfer objects. A C# record with init-only properties is ideal for JSON deserialization when immutability is desired. The converter can generate records instead of classes — syntax is similar, but record types automatically implement value equality (two records with the same properties are equal) and provide with-expressions for non-destructive mutation.

When developers use this tool

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