diff --git a/PLAN.md b/PLAN.md
index 38d0643..72ca092 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -4,6 +4,8 @@
 
 `Yonexus.Client` is the OpenClaw plugin that acts as a client in a Yonexus network.
 
+This repository references `Yonexus.Protocol` as a submodule at `protocol/`.
+
 It is responsible for:
 - connecting to `Yonexus.Server`
 - managing local keypair and secret