diff --git a/src/oss/langchain/middleware.mdx b/src/oss/langchain/middleware.mdx
index 929b7ff5b8..d9dad1d522 100644
--- a/src/oss/langchain/middleware.mdx
+++ b/src/oss/langchain/middleware.mdx
@@ -1044,6 +1044,12 @@ Use an LLM to intelligently select relevant tools before calling the main model.
     - Improving model focus and accuracy
 </Tip>
 
+<Note>
+    **How it works:** This middleware uses structured output to ask an LLM which tools are most relevant for the current query. The structured output schema defines the available tool names and descriptions.
+
+    Model providers often add this structured output information to the system prompt behind the scenes.
+</Note>
+
 :::python
 ```python
 from langchain.agents import create_agent