diff --git a/nanobot/agent/tools/message.py b/nanobot/agent/tools/message.py
index 0a52427..c8d50cf 100644
--- a/nanobot/agent/tools/message.py
+++ b/nanobot/agent/tools/message.py
@@ -42,7 +42,12 @@ class MessageTool(Tool):
 
     @property
     def description(self) -> str:
-        return "Send a message to the user. Use this when you want to communicate something."
+        return (
+            "Send a message to the user, optionally with file attachments. "
+            "This is the ONLY way to deliver files (images, documents, audio, video) to the user. "
+            "Use the 'media' parameter with file paths to attach files. "
+            "Do NOT use read_file to send files — that only reads content for your own analysis."
+        )
 
     @property
     def parameters(self) -> dict[str, Any]: