Use Namespace Newtonsoft.Json.Formatting Newtonsoft.Json.Formatting provides formatting options to Format the Json

None − No special formatting is applied. This is the default.

Indented − Causes child objects to be indented according to the Newtonsoft.Json.JsonTextWriter.Indentation and Newtonsoft.Json.JsonTextWriter.IndentChar settings.

static void Main(string[] args){
   Product product = new Product{
      Name = "Samsung",
      Expiry = new DateTime(2008, 12, 28),
      Price = 3.9900M,
      Sizes = new[] { "Small", "Medium", "Large" }
   };
   string json = JsonConvert.SerializeObject(product, Formatting.Indented);
   Console.WriteLine(json);
   Product deserializedProduct = JsonConvert.DeserializeObject<Product>(json);
   Console.ReadLine();
}
class Product{
   public String[] Sizes { get; set; }
   public decimal Price { get; set; }
   public DateTime Expiry { get; set; }
   public string Name { get; set; }
}