<project outputDir="outputDir" baseDir="baseDir" seed="seednumber" xmlns="http://confuser.codeplex.com">
  <rule pattern="true" inherit="false">
    <protection id="ctrl flow" />
    <protection id="rename" />
  </rule>
  <module path="ConfuserTests.exe" />
</project>

using System.Reflection;
using Newtonsoft.Json;

namespace ConfuserTests
{
  [Obfuscation(Exclude = true)]
  public class Obf
  {
    [JsonProperty("a")] public string a;

    [JsonProperty("b")] public string b;

    [JsonProperty("c")] public string c;

    public Obf(string a, string b, string c){
      this.a = a;
      this.b = b;
      this.c = c;
    }
    
    public override string ToString(){
      return JsonConvert.SerializeObject(this);
    }
  }
}

    public static void Main(string[] args){

      try{
        Obf a = new Obf("a","b","c");
        string obfstring = a.ToString();
        Console.WriteLine(obfstring);
      }
      catch (Exception e){
        Console.WriteLine(e);
      }
      
      Console.ReadLine();
    }

Newtonsoft.Json.JsonSerializationException: A member with the name '' already exists on 'ConfuserTests.Obf'. Use the JsonPropertyAttribute to specify another name.
   at Newtonsoft.Json.Serialization.JsonPropertyCollection.AddProperty(JsonProperty property)
   at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateConstructorParameters(ConstructorInfo constructor, JsonPropertyCollection memberProperties)
   at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateObjectContract(Type objectType)
   at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateContract(Type objectType)
   at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at Newtonsoft.Json.Serialization.DefaultContractResolver.ResolveContract(Type type)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType)
   at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType)
   at Newtonsoft.Json.JsonConvert.SerializeObjectInternal(Object value, Type type, JsonSerializer jsonSerializer)
   at Newtonsoft.Json.JsonConvert.SerializeObject(Object value)
   at ConfuserTests.Obf.?????????????????????????????????????????() in C:\path\ConfuserTests\Obf.cs:line 25
   at ?????????????????????????????????????????.?????????????????????????????????????????(String[] ) in C:\path\ConfuserTests\Program.cs:line 11