diff --git a/lang_agent/base.py b/lang_agent/base.py
index 5aa6506..3c17c00 100644
--- a/lang_agent/base.py
+++ b/lang_agent/base.py
@@ -13,4 +13,11 @@ class GraphBase(ABC):
     
     @abstractmethod
     def invoke(self, *nargs, **kwargs):
+        pass
+
+
+class ToolNodeBase(ABC):
+
+    @abstractmethod
+    def tool_node_call(self, *nargs, **kwargs):
         pass
\ No newline at end of file