using System;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        var json = @"{

            ""stringValue"" :   0.0050000012852251529693603515625,

            ""decimalValue"" :  0.0050000012852251529693603515625,

            ""bigDecimalValue"" : 0.0050000012852251529693603515625

        }";

​

        var settings = new JsonSerializerSettings();

        settings.FloatParseHandling = FloatParseHandling.Decimal;

        settings.Converters.Add(new JsonBigDecimalConverter());

​

        var result = JsonConvert.DeserializeObject<DecimalTest>(json, settings);

​

        AssertAreEqual("0.0050000012852251529693603515625", result.stringValue, "stringValue");

        AssertAreEqual(0.0050000012852251529693603516m, result.decimalValue, "decimalValue");

        AssertAreEqual("0.0050000012852251529693603515625", result.bigDecimalValue.ToString(), "bigDecimalValue");

        Console.WriteLine("All tests passed.");

    }

    public static void AssertAreEqual<T>(T expected, T actual, string name = null)

    {

        if (!expected.Equals(actual))

            throw new Exception("Asserting '" + (name) + "' failed. Expected: " + expected + ", actual: " + actual);

    }

}

​

public class DecimalTest

{

    public string stringValue { get; set; }

    public decimal decimalValue { get; set; }

    public BigDecimal bigDecimalValue { get; set; }

}

​

public class BigDecimal

{

    public string Value { get; set; }

    public static BigDecimal Parse(string str)

    {

        return new BigDecimal { Value = str };

    }

}

​

public class JsonBigDecimalConverter : JsonConverter

{

    public override bool CanConvert(Type objectType)

    {

        return (objectType == typeof(BigDecimal));

    }

​

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

    {

        var token = JToken.Load(reader);

        return BigDecimal.Parse(token.ToString());

    }

​

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

    {

        throw new NotImplementedException();

    }

}