diff --git a/tractor/msg/types.py b/tractor/msg/types.py
index 63c0a46..7e10dab 100644
--- a/tractor/msg/types.py
+++ b/tractor/msg/types.py
@@ -144,6 +144,8 @@ class SpawnSpec(
     `Aid` msg.
 
     '''
+    # TODO: similar to the `Start` kwargs spec needed below, we need
+    # a hard `Struct` def for all of these fields!
     _parent_main_data: dict
     _runtime_vars: dict[str, Any]