diff --git a/docs/realtime.md b/docs/realtime.md
index fbca941..d1b78d0 100644
--- a/docs/realtime.md
+++ b/docs/realtime.md
@@ -56,6 +56,8 @@ Supported `type` values:
 
 - `text`, `image`, `video`, `audio`, `voice`, `file`, `circle_video`
 
+Web note: browser client sends `text/image/video/audio/voice/file`. `circle_video` is reserved for mobile clients.
+
 ## 2.3 `typing_start` / `typing_stop`
 
 ```json