public class CustomContractResolver : DefaultContractResolver
    {
        protected override JsonContract CreateContract(Type objectType)
        {
            var contract = base.CreateContract(objectType);

            if (objectType == typeof(decimal))
            {
                //Not sure this will actually give you the attribute, haven't tested it
                var custom = objectType.GetCustomAttributes(true).OfType<AvroFieldAttribute>().SingleOrDefault();
                if (custom != null)
                {
                    contract.Converter = new AvroDecimalJsonConverter(custom.Precision, custom.Scale);
                }

            }

            return contract;
        }
    }