diff --git a/include/wrapper/ArgsFromClient.hpp b/include/wrapper/ArgsFromClient.hpp
index 88ae458..7e49cab 100644
--- a/include/wrapper/ArgsFromClient.hpp
+++ b/include/wrapper/ArgsFromClient.hpp
@@ -135,38 +135,45 @@ struct ParamReader<sc_msg_iter>
     }
   }
   
-  static const char* argTypeToString(std::string&)
+  
+  template <typename T>
+  static const char* argTypeToString(Optional<T>&)
+  {
+    return argTypeToString(T{});
+  }
+  
+  static const char* argTypeToString(const std::string&)
   {
     return "string";
   }
   
   template <typename T>
   static std::enable_if_t<std::is_integral<T>::value, const char*>
-  argTypeToString(T&)
+  argTypeToString(T)
   {
     return "integer";
   }
 
   template <typename T>
   static std::enable_if_t<std::is_floating_point<T>::value, const char*>
-  argTypeToString(T&)
+  argTypeToString(T)
   {
     return "float";
   }
 
-  static const char* argTypeToString(BufferT::type&)
+  static const char* argTypeToString(const BufferT::type&)
   {
     return "buffer";
   }
   
-  static const char* argTypeToString(InputBufferT::type&)
+  static const char* argTypeToString(const InputBufferT::type&)
   {
     return "buffer";
   }
   
   template <typename P>
   static std::enable_if_t<IsSharedClient<P>::value,const char*>
-  argTypeToString(P&)
+  argTypeToString(const P&)
   {
     return "shared_object"; //not ideal
   }
@@ -179,28 +186,34 @@ struct ParamReader<sc_msg_iter>
   template <typename T>
   static std::enable_if_t<std::is_integral<T>::value
                           || std::is_floating_point<T>::value, bool>
-  argTypeOK(T&, char tag)
+  argTypeOK(T, char tag)
   {
     return tag == 'i' || tag == 'f' || tag == 'd';
   }
 
-  static bool argTypeOK(BufferT::type&, char tag)
+  static bool argTypeOK(const BufferT::type&, char tag)
   {
     return tag == 'i';
   }
   
-  static bool argTypeOK(InputBufferT::type&, char tag)
+  static bool argTypeOK(const InputBufferT::type&, char tag)
   {
     return tag == 'i';
   }
   
   template <typename P>
   static std::enable_if_t<IsSharedClient<P>::value,bool>
-  argTypeOK(P&, char tag)
+  argTypeOK(const P&, char tag)
   {
     return tag == 'i';
   }
   
+  template<typename T>
+  static bool argTypeOK(const Optional<T>&, char tag)
+  {
+    return argTypeOK(T{},tag);
+  }
+  
   static auto fromArgs(World*, sc_msg_iter& args, std::string, int)
   {
     const char* recv = args.gets("");
@@ -266,6 +279,13 @@ struct ParamReader<sc_msg_iter>
         res[i] = static_cast<Value>(args.geti());
       return res;
   }
+  
+  template<typename T>
+  static auto fromArgs(World* w, sc_msg_iter& args, Optional<T>, int)
+  {
+    return Optional<T>{fromArgs(w,args,T{},int{})};
+  }
+  
 };
 
 
diff --git a/include/wrapper/Messaging.hpp b/include/wrapper/Messaging.hpp
index 77c4d05..ef5ee8b 100644
--- a/include/wrapper/Messaging.hpp
+++ b/include/wrapper/Messaging.hpp
@@ -48,10 +48,27 @@ struct FluidSCMessaging{
   };
   
 
+
+  template<typename T>
+  static auto constexpr filterOneOptional(const T&) { return std::make_tuple(T{}); }
+
+  template<typename T>
+  static auto constexpr filterOneOptional(const Optional<T>&) { return std::make_tuple(); }
+  
+  
+  template<typename...Ts>
+  static auto constexpr filterOptional(std::tuple<Ts...>)
+  {
+    return std::tuple_cat(filterOneOptional(Ts{})...);
+  }
+  
+  
   template <typename Message>
-  static bool validateMessageArgs(Message* msg, sc_msg_iter* inArgs)
+  static Optional<size_t> validateMessageArgs(Message* msg, sc_msg_iter* inArgs)
   {
+    //we can be sure that optional args always follow mandatory ones, as this is enforced at compile time in flucoma-core
     using ArgTuple = decltype(msg->args);
+    using MandatoryArgsTuple = decltype(filterOptional(msg->args));
     
     std::string tags(inArgs->tags + inArgs->count);//evidently this needs commenting: construct string at pointer offset by tag count, to pick up args
     bool willContinue = true;
@@ -59,7 +76,7 @@ struct FluidSCMessaging{
     
     auto& args = msg->args;
     
-    constexpr size_t expectedArgCount = std::tuple_size<ArgTuple>::value;
+    constexpr size_t expectedArgCount = std::tuple_size<MandatoryArgsTuple>::value;
     
     /// TODO this squawks if we have a completion message, so maybe we can check if extra arg is a 'b' and squawk if not?
 //    if(tags.size() > expectedArgCount)
@@ -77,14 +94,16 @@ struct FluidSCMessaging{
 
     auto tagsIter = tags.begin();
     auto tagsEnd  = tags.end();
-    ForEach(args,[&typesMatch,&tagsIter,&tagsEnd](auto& arg){
+    size_t argCount = 0;
+    ForEach(args,[&typesMatch,&tagsIter,&tagsEnd,firstTag=tags.begin(),&argCount](auto& arg){
        if(tagsIter == tagsEnd)
        {
-          typesMatch = false;
+          if(std::distance(firstTag,tagsIter) < expectedArgCount) typesMatch = false;
           return;
        }
        char t = *(tagsIter++);
        typesMatch = typesMatch && ParamReader<sc_msg_iter>::argTypeOK(arg,t);
+       argCount++;
     });
     
    willContinue = willContinue && typesMatch;
@@ -116,7 +135,7 @@ struct FluidSCMessaging{
       report << ")\n";
    }
    
-   return willContinue;
+   return willContinue ?  Optional<size_t>(argCount) : Optional<size_t>();
   }
 
   static void refreshParams(Params& p, MessageResult<ParamValues>& r)
@@ -137,9 +156,9 @@ struct FluidSCMessaging{
     msg->id = args->geti();
     msg->replyAddr = copyReplyAddress(replyAddr);
     ///TODO make this step contingent on verbosity or something, in the name of effieciency
-    bool willContinue = validateMessageArgs(msg, args);
+    auto tagCount = validateMessageArgs(msg, args);
     
-    if(!willContinue)
+    if(!tagCount.has_value())
     {
       delete msg;
       return;
@@ -148,9 +167,10 @@ struct FluidSCMessaging{
 
     msg->name = std::string{'/'} +  (const char*)(inUserData);
     
-    ForEach(msg-> args,[inWorld,&args](auto& thisarg)
+    ForEach(msg-> args,[inWorld,&args,tagCount,n=0](auto& thisarg)mutable
     {
-      thisarg = ParamReader<sc_msg_iter>::fromArgs(inWorld, *args,thisarg,0);
+      if(n++ <  tagCount.value())
+        thisarg = ParamReader<sc_msg_iter>::fromArgs(inWorld, *args,thisarg,0);
     });
      
     size_t completionMsgSize{args ? args->getbsize() : 0};
diff --git a/release-packaging/Classes/FluidKDTree.sc b/release-packaging/Classes/FluidKDTree.sc
index 8ce1aac..3dc3c04 100644
--- a/release-packaging/Classes/FluidKDTree.sc
+++ b/release-packaging/Classes/FluidKDTree.sc
@@ -24,13 +24,16 @@ FluidKDTree : FluidModelObject
 		this.prSendMsg(this.fitMsg(dataSet));
 	}
 
-    kNearestMsg{|buffer|
-        ^this.prMakeMsg(\kNearest,id,this.prEncodeBuffer(buffer));
+    kNearestMsg{|buffer,k|
+        k !?
+        {^this.prMakeMsg(\kNearest,id,this.prEncodeBuffer(buffer),k);}
+        ??
+        {^this.prMakeMsg(\kNearest,id,this.prEncodeBuffer(buffer));}
     }
 
-	kNearest{ |buffer, action|
+	kNearest{ |buffer, k, action|
         actions[\kNearest] = [strings(FluidMessageResponse,_,_),action];
-		this.prSendMsg(this.kNearestMsg(buffer));
+		this.prSendMsg(this.kNearestMsg(buffer,k));
 	}
 
     kNearestDistMsg {|buffer|