json-example.cs

using System;
using System.Text.Json;
using System.Text.Json.Serialization;

User? user = JsonSerializer.Deserialize<User>(
    await new HttpClient().GetStringAsync("https://jsonplaceholder.typicode.com/todos/1"), MyJsonContext.Default.User);

Console.WriteLine($"id={user?.id}, title={user?.title}");

public record User(int userId, int id, string title, bool completed);





[JsonSerializable(typeof(User))]
internal partial class MyJsonContext : JsonSerializerContext {}