JSON to C# Class

Example output

For input:

{ "firstName": "Alice", "age": 30, "emails": ["a@a.com"], "address": { "city": "Madrid" } }

System.Text.Json output (C# 10+):

public class User
{
    [JsonPropertyName("firstName")]
    public string FirstName { get; set; } = default!;

    [JsonPropertyName("age")]
    public int Age { get; set; }

    [JsonPropertyName("emails")]
    public List<string> Emails { get; set; } = new();

    [JsonPropertyName("address")]
    public Address Address { get; set; } = default!;
}

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

Type mapping

Attribute options

• System.Text.Json ([JsonPropertyName("foo")]), preferred for .NET 6+ and new projects.
• Newtonsoft.Json ([JsonProperty("foo")]), for legacy projects or when you need Newtonsoft-specific features.
• None, property names match JSON keys exactly (works only if JSON keys are PascalCase already).

Common mistakes

• Using int for a field that might overflow. If your JSON has values that exceed int.MaxValue, use long. The generator promotes automatically when it sees large values.
• Missing [JsonIgnore] for computed properties. If you add helper props to the generated class, decorate them with [JsonIgnore] or they will serialize on the way out.
• Forgetting culture-invariant parsing. decimal fields should deserialize with CultureInfo.InvariantCulture; System.Text.Json does this by default, Newtonsoft with global settings.
• Trusting the generator with one sample. Nullability and array-item types are guessed from what it sees. Always sanity-check nullable annotations against your actual API behaviour.