diff --git a/UI.tscn b/UI.tscn
index 3066733..fe2ae17 100644
--- a/UI.tscn
+++ b/UI.tscn
@@ -24,7 +24,6 @@ anchor_bottom = 1.0
 grow_horizontal = 2
 grow_vertical = 2
 script = ExtResource("1_28t32")
-osc_dest_port = 9001
 debug = true
 
 [node name="MarginContainer" type="MarginContainer" parent="."]
diff --git a/osc_receiver.gd b/osc_receiver.gd
index 9feaf32..e73353c 100644
--- a/osc_receiver.gd
+++ b/osc_receiver.gd
@@ -26,14 +26,14 @@ func _exit_tree():
 	stop_server()
 
 
-func register_callback(oscaddress, argtypes, callback):
-	if not _observers.has([oscaddress, argtypes]):
-		_observers[[oscaddress, argtypes]] = []
+func register_callback(osc_address, arg_types, callback) -> void:
+	if not _observers.has([osc_address, arg_types]):
+		_observers[[osc_address, arg_types]] = []
 
-	_observers[[oscaddress, argtypes]].append(callback)
+	_observers[[osc_address, arg_types]].append(callback)
 
 
-func start_server(port:int = default_port, bind_address:String = default_address):
+func start_server(port:int = default_port, bind_address:String = default_address) -> void:
 	_server = UDPServer.new()
 
 	if _server.listen(port, bind_address) != OK:
@@ -44,7 +44,7 @@ func start_server(port:int = default_port, bind_address:String = default_address
 	_timer.start(poll_interval)
 
 
-func stop_server():
+func stop_server() -> void:
 	_timer.stop()
 	remove_child(_timer)
 	_timer.free()
@@ -53,12 +53,12 @@ func stop_server():
 		_server.stop()
 
 
-func _debug(msg):
+func _debug(msg) -> void:
 	if debug:
 		print(msg)
 
 
-func _poll():
+func _poll() -> void:
 	if not _server.is_listening():
 		return
 
@@ -81,11 +81,11 @@ func _poll():
 		_debug("OSC arg types: %s" % types)
 
 		if _observers.has([address, types]):
-			var values = _parse_osc_values(packet.slice(offset), types)
+			result = _parse_osc_values(packet.slice(offset), types)
 
-			if values == null:
+			if result[0] != OK:
 				_debug("Invalid/Unsupported OSC message.")
-			elif values.size() != types.length():
+			elif result[1].size() != types.length():
 				_debug("Mismatch between expected / received number of OSC arguments.")
 			else:
 				var msg_info = {
@@ -96,9 +96,9 @@ func _poll():
 				}
 
 				for callback in _observers[[address, types]]:
-					callback.call(msg_info, values)
+					callback.call(msg_info, result[1])
 
-func _parse_osc_addr_and_types(packet: PackedByteArray):
+func _parse_osc_addr_and_types(packet: PackedByteArray) -> Array:
 	var asep = packet.find(0)
 	var address = packet.slice(0, asep).get_string_from_ascii() 
 	
@@ -110,7 +110,7 @@ func _parse_osc_addr_and_types(packet: PackedByteArray):
 	return [address, types, tsep + (4 - tsep % 4)]
 
 
-func _parse_osc_values(packet: PackedByteArray, types: String):
+func _parse_osc_values(packet: PackedByteArray, types: String) -> Array:
 	var result
 	var values = []
 	var stream = StreamPeerBuffer.new()
@@ -153,7 +153,7 @@ func _parse_osc_values(packet: PackedByteArray, types: String):
 						stream.seek(stream.get_position() + (4 - count % 4))
 				else:
 					_debug("Could not read OSC blob argument.")
-					return
+					return [ERR_PARSE_ERROR]
 			"t":
 				result = stream.get_data(8)
 
@@ -161,7 +161,7 @@ func _parse_osc_values(packet: PackedByteArray, types: String):
 					values.append(result[1])
 				else:
 					_debug("Could not read OSC timetag argument.")
-					return
+					return [ERR_PARSE_ERROR]
 			"m", "r":
 				values.append([
 					stream.get_u8(),
@@ -177,6 +177,6 @@ func _parse_osc_values(packet: PackedByteArray, types: String):
 				values.append(null)
 			_:
 				_debug("Argument type '%s' not supported." % type_id)
-				return
+				return [ERR_INVALID_DATA]
 
-	return values
+	return [OK, values]
diff --git a/osc_sender.gd b/osc_sender.gd
index b907569..935ff1e 100644
--- a/osc_sender.gd
+++ b/osc_sender.gd
@@ -17,12 +17,12 @@ func _init():
 	_socket.set_dest_address(_address, _port)
 
 
-func _debug(msg):
+func _debug(msg) -> void:
 	if debug:
 		print(msg)
 
 
-func set_destination(dest):
+func set_destination(dest) -> void:
 	if dest is int:
 		_socket.set_dest_address(_address, dest)
 		_port = dest
@@ -35,16 +35,18 @@ func set_destination(dest):
 		_port = dest[1]
 
 
-func send_osc(oscaddress: String, argtypes: String, values: Array, dest = null):
-	assert(oscaddress.begins_with("/"))
+func create_message(osc_address: String, arg_types: String, values: Array) -> Array:
+	if not osc_address.begins_with("/"):
+		return [ERR_INVALID_DATA]
+
 	var buf = StreamPeerBuffer.new()
 	buf.set_big_endian(true)
-	_pack_string(buf, oscaddress)
-	_pack_string(buf, "," + argtypes)
+	_pack_string(buf, osc_address)
+	_pack_string(buf, "," + arg_types)
 	var vidx: int = 0
 
-	for i in argtypes.length():
-		var typetag = argtypes[i]
+	for i in arg_types.length():
+		var typetag = arg_types[i]
 		var inc_vidx = true
 
 		match typetag:
@@ -72,19 +74,28 @@ func send_osc(oscaddress: String, argtypes: String, values: Array, dest = null):
 				inc_vidx = false  # no argument value sent
 			_:
 				_debug("Argument type '%s' not supported." % typetag)
-				return FAILED
+				return [ERR_INVALID_PARAMETER]
 
 		if inc_vidx:
 			vidx += 1
 
+	return [OK, buf.get_data_array()]
+
+
+func send_osc(osc_address: String, arg_types: String, values: Array, dest = null) -> Error:
+	var res = create_message(osc_address, arg_types, values)
+
+	if res[0] != OK:
+		return res[0]
+
 	if dest != null:
 		set_destination(dest)
 
-	_socket.put_packet(buf.get_data_array())
+	_socket.put_packet(res[1])
 	return OK
 
 
-func _pack_string(buf: StreamPeerBuffer, s: String):
+func _pack_string(buf: StreamPeerBuffer, s: String) -> void:
 	## Pack a string into a binary OSC buffer
 	buf.put_data(s.to_ascii_buffer())
 
@@ -93,7 +104,7 @@ func _pack_string(buf: StreamPeerBuffer, s: String):
 		buf.put_u8(0)
 
 
-func _pack_blob(buf, blob):
+func _pack_blob(buf, blob) -> void:
 	## Pack a PackedByteArray, Array or String into a binary OSC buffer
 	if blob is String:
 		blob = blob.to_utf8_buffer()
diff --git a/screenshot.png b/screenshot.png
new file mode 100644
index 0000000..0837de5
Binary files /dev/null and b/screenshot.png differ
diff --git a/screenshot.png.import b/screenshot.png.import
new file mode 100644
index 0000000..df499f9
--- /dev/null
+++ b/screenshot.png.import
@@ -0,0 +1,34 @@
+[remap]
+
+importer="texture"
+type="CompressedTexture2D"
+uid="uid://bc0u3ivd6q1jg"
+path="res://.godot/imported/screenshot.png-024a21af5d37bf0f0dd0e2bccdd149d0.ctex"
+metadata={
+"vram_texture": false
+}
+
+[deps]
+
+source_file="res://screenshot.png"
+dest_files=["res://.godot/imported/screenshot.png-024a21af5d37bf0f0dd0e2bccdd149d0.ctex"]
+
+[params]
+
+compress/mode=0
+compress/high_quality=false
+compress/lossy_quality=0.7
+compress/hdr_compression=1
+compress/normal_map=0
+compress/channel_pack=0
+mipmaps/generate=false
+mipmaps/limit=-1
+roughness/mode=0
+roughness/src_normal=""
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/normal_map_invert_y=false
+process/hdr_as_srgb=false
+process/hdr_clamp_exposure=false
+process/size_limit=0
+detect_3d/compress_to=1
diff --git a/slider.gd b/slider.gd
index 94de797..acf52e0 100644
--- a/slider.gd
+++ b/slider.gd
@@ -1,9 +1,5 @@
 extends VSlider
 
 
-func recv_osc(msg_info, values):
-	#print("Sender IP: %s" % msg_info["ip"])
-	#print("Sender Port: %d" % msg_info["port"])
-	#print("Address: %s" % msg_info["address"])
-	#print("Types: %s" % msg_info["types"])
+func recv_osc(msg_info, values) -> void:
 	set_value_no_signal(clampf(values[0], 0.0, 1.0))
diff --git a/toggle_button.gd b/toggle_button.gd
index eb90c5a..5aff3f3 100644
--- a/toggle_button.gd
+++ b/toggle_button.gd
@@ -1,9 +1,5 @@
 extends Button
 
 
-func recv_osc(msg_info, values):
-	#print("Sender IP: %s" % msg_info["ip"])
-	#print("Sender Port: %d" % msg_info["port"])
-	#print("Address: %s" % msg_info["address"])
-	#print("Types: %s" % msg_info["types"])
+func recv_osc(msg_info, values) -> void:
 	set_pressed_no_signal(bool(values[0]))
diff --git a/ui.gd b/ui.gd
index e06b204..e27cad9 100644
--- a/ui.gd
+++ b/ui.gd
@@ -27,33 +27,40 @@ func _ready():
 	# configure all sensors
 	for i in range(4):
 		var nodename = "VSlider%d" % (i + 1)
-		var osc_addr = "/slider/%d" % i
+		var osc_address = "/slider/%d" % i
 		var slider_node = find_child(nodename)
-		osc_server.register_callback(osc_addr, "f", slider_node.recv_osc)
+		osc_server.register_callback(osc_address, "f", slider_node.recv_osc)
 		slider_node.value_changed.connect(slider_callback.bind(i))
+	
+		if debug:
+			osc_server.register_callback(osc_address, "f", print_osc_message)
 
 	for i in range(4):
 		var nodename = "Button%d" % (i + 1)
-		var osc_addr = "/button/%d" % i
+		var osc_address = "/button/%d" % i
 		var button_node = find_child(nodename)
-		osc_server.register_callback(osc_addr, "i", button_node.recv_osc)
 		button_node.pressed.connect(button_callback.bind(button_node, i))
+		osc_server.register_callback(osc_address, "i", button_node.recv_osc)
+
+		if debug:
+			osc_server.register_callback(osc_address, "i", print_osc_message)
 
 	# start listening for osc messages
 	osc_server.start_server(osc_server_port, osc_server_address)
 
 
-func _button_pressed(btn: Button, idx: int):
-	_debug("Button %s pressed: state = %s" % [idx, btn.button_pressed])
-	osc_client.send_osc("/button/%d" % idx, "i", [1 if btn.button_pressed else 0])
+func _button_pressed(btn: Button, idx: int) -> void:
+	var value = 1 if btn.button_pressed else 0
+	_debug("Button %s pressed: value = %s" % [idx, value])
+	osc_client.send_osc("/button/%d" % idx, "i", [value])
 
 
-func _slider_moved(value: float, idx: int):
+func _slider_moved(value: float, idx: int) -> void:
 	_debug("Slider %d moved: value = %f" % [idx, value])
 	osc_client.send_osc("/slider/%d" % idx, "f", [value])
 
 
-func recv_osc(msg_info, values):
+func print_osc_message(msg_info, values) -> void:
 	_debug("Sender IP: %s" % msg_info["ip"])
 	_debug("Sender Port: %d" % msg_info["port"])
 	_debug("Address: %s" % msg_info["address"])
@@ -61,6 +68,6 @@ func recv_osc(msg_info, values):
 	_debug("Values: %s" % values)
 
 
-func _debug(msg):
+func _debug(msg) -> void:
 	if debug:
 		print(msg)