using System;

using System.Linq;

using System.Collections.Generic;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        //string jsonContent = "[{\"fields\":[[{\"letter\":\"A\", \"certainty\":\"B\"}]], \"success\":\"Y\",\"message\":\"Access is granted\"}]";

        string jsonContent = "{\"fields\":[[{\"letter\":\"A\", \"certainty\":\"B\"}]], \"success\":\"Y\",\"message\":\"Access is granted\"}";

        //var zz =    JsonConvert.DeserializeObject<List<MyArray>>(jsonContent);

        var zz =    JsonConvert.DeserializeObject<MyArray>(jsonContent);

        //Console.WriteLine(zz[0].fields[0][0].letter);

        Console.WriteLine(zz.fields[0][0].letter);

    }

}

​

public class MyArray

    {

        public List<List<Test>> fields { get; set; }

        public string success { get; set; }

        public string message { get; set; }

    }

public class Test

{

    public string letter {get;set;}

    public string certainty {get;set;}

}

    public class Root

    {

        public List<MyArray> MyArray { get; set; }

    }