Convert JSON to C# Classes: System.Text.Json vs Newtonsoft

Start from a sample object

Paste one representative JSON object. The generator creates a class for the root and a class for each nested object, and arrays become List<T>.

{
  "id": 42,
  "user_name": "ada",
  "is_active": true,
  "tags": ["dev", "math"]
}

Map JSON names to C# names

In the JSON to C# Converter, the Property attributes menu adds either style to every property.

// System.Text.Json
using System.Text.Json.Serialization;
public class User {
    [JsonPropertyName("id")]        public int Id { get; set; }
    [JsonPropertyName("user_name")] public string UserName { get; set; }
}

// Newtonsoft.Json
using Newtonsoft.Json;
public class User {
    [JsonProperty("id")]        public int Id { get; set; }
    [JsonProperty("user_name")] public string UserName { get; set; }
}

Case sensitivity: the usual surprise

System.Text.Json matches property names case-sensitively by default, so "name" will not fill a property called Name unless you opt in. Newtonsoft.Json matches case-insensitively by default.

• To map snake_case keys without an attribute on every property, set PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower (.NET 8 and later).

var options = new JsonSerializerOptions {
    PropertyNameCaseInsensitive = true,
    PropertyNamingPolicy = JsonNamingPolicy.CamelCase
};
var user = JsonSerializer.Deserialize<User>(json, options);

Fix the types a sample cannot reveal

• Numbers: one sample cannot tell int from long, double or decimal. Use decimal for money, long for large IDs, int for small counts.
• Nullable values: a null or missing field needs a nullable type, such as string? or int?.
• Dates: ISO 8601 strings such as 2026-11-01T10:00:00Z deserialize into DateTime or DateTimeOffset.
• Arrays of mixed types: the generator cannot infer a single type, so define a proper model.
• Keys that are C# keywords, such as class or event, need an @ prefix or an attribute.

Records for immutable models

For read-only data transfer objects, a positional record is shorter. System.Text.Json can deserialize records through their constructor.

public record User(int Id, string UserName, bool IsActive, List<string> Tags);