using System;

using System.Text.Json;

using System.Text.Json.Serialization;

public class Program

{

    public static void Main()

    {

        var json = @"{

            ""number1"": 0.00000000,

            ""number2"": 749294.8482800084720000000

        }";

        // adding converter using the options for demo, but you can register it in services.Config

        var options = new JsonSerializerOptions(){ Converters = { new DecimalJsonConverter() }};

        // deserialize

        var model = JsonSerializer.Deserialize<Model>(json, options);

        model.Dump();

        // serialize

        var model2 = new Model { Number1 = 0.000000m, Number2 = 123.456000000m };

        var serialized = JsonSerializer.Serialize(model2, options);

        serialized.Dump();

    }

}

​

public class DecimalJsonConverter : JsonConverter<decimal>

    {

        public override decimal Read(

            ref Utf8JsonReader reader, 

            Type typeToConvert, 

            JsonSerializerOptions options) =>

                reader.GetDecimal().Normalize();

​

        public override void Write(

            Utf8JsonWriter writer, 

            decimal value, 

            JsonSerializerOptions options) =>         

                writer.WriteNumberValue(value.Normalize());        

    }

​

public static class ExtensionMethods 

{

    public static decimal Normalize(this decimal value) =>

        value / 1.000000000000000000000000000000000m;

}

​

public class Model

{

    [JsonPropertyName("number1")]

    public decimal Number1 { get; set; }

    [JsonPropertyName("number2")]

    public decimal Number2 { get; set; }

}