using System;

using System.Collections.Generic;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var obj = new

        {

            name = "Mary",

            isMale = false,

            likesPonies = true

        };

​

        JsonSerializerSettings settings = new JsonSerializerSettings

        {

            Converters = new List<JsonConverter> { new BoolToStringConverter() },

            Formatting = Formatting.Indented

        };

​

        var json = JsonConvert.SerializeObject(obj, settings);

        Console.WriteLine(json);

    }

}

​

public class BoolToStringConverter : JsonConverter

{

    public override bool CanConvert(Type objectType)

    {

        return objectType == typeof(bool);

    }

​

    public override bool CanRead

    {

        get { return false; }

    }

​

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)

    {

        throw new NotImplementedException();

    }

​

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)

    {

        writer.WriteValue((bool)value ? "true" : "false");

    }

}

​