JSON to C#

Attributes that are actually needed

By default the generator only writes a name attribute when the C# property name differs from the JSON key. That keeps the output readable — but it is worth knowing why the attribute is required in those cases: System.Text.Json matches property names case-sensitively unless you configure otherwise, so Id would silently come back as 0 from a payload containing "id".

public class Root
{
    [JsonPropertyName("id")]
    public long Id { get; set; }

    [JsonPropertyName("isActive")]
    public bool IsActive { get; set; }

    [JsonPropertyName("website")]
    public string? Website { get; set; }
}

Turn on Attribute every property if your team prefers explicit mapping on every member, or if you are serialising into a system where the casing rules are not under your control.

Class or record

Classes use mutable auto-properties, which is what most serialisers and ORMs expect. Records are positional and immutable — shorter and better for value-like payloads, but the constructor arguments must be matched by name, so the attribute becomes a property: target:

public record Root(
    [property: JsonPropertyName("id")] long Id,
    [property: JsonPropertyName("name")] string Name
);

Type mapping

The ? annotations need a nullable context

A question mark on a reference type is only meaningful when nullable reference types are enabled. Add this to your .csproj, or the compiler will warn:

<PropertyGroup>
  <Nullable>enable</Nullable>
  <LangVersion>latest</LangVersion>
</PropertyGroup>

Deserialising the payload

var options = new JsonSerializerOptions { PropertyNameCaseInsensitive = true };
var payload = JsonSerializer.Deserialize<Root>(body, options);
Console.WriteLine(payload?.Address?.City);

Edge cases worth knowing

• Newtonsoft versus System.Text.Json. The only difference in the output is the attribute name and namespace — [JsonProperty] from Newtonsoft.Json versus [JsonPropertyName] from System.Text.Json.Serialization.
• C# naming keeps Id, not ID. That matches the .NET framework design guidelines; the wire spelling is preserved by the attribute.
• A key that starts with a digit is not a legal C# identifier, so it gains an underscore (_2fa) and the attribute carries the real key.
• Mixed arrays become List<object>; there is no common base type to describe [1, "two"] more precisely.

FAQ