diff --git a/libs/prebuilt/langgraph/prebuilt/tool_node.py b/libs/prebuilt/langgraph/prebuilt/tool_node.py
index 425ee38b0..a6d2e4fd6 100644
--- a/libs/prebuilt/langgraph/prebuilt/tool_node.py
+++ b/libs/prebuilt/langgraph/prebuilt/tool_node.py
@@ -615,7 +615,7 @@ class ToolNode(RunnableCallable):
     error handling.
 
     Input Formats:
-        1. Graph state with `messages` key that has a list of messages:
+        1. **Graph state** with `messages` key that has a list of messages:
             - Common representation for agentic workflows
             - Supports custom messages key via `messages_key` parameter