diff --git a/rfc/0004_ws2p_v1.md b/rfc/0004_ws2p_v1.md
index 136bfd92f9be739aefb155d696817e68685628f2..916ad9e77ef8a1853a1101ee5800b9c72e6aa206 100644
--- a/rfc/0004_ws2p_v1.md
+++ b/rfc/0004_ws2p_v1.md
@@ -225,6 +225,19 @@ The set of heads known by a duniter node at the moment is public information ava
 
 Each new head received from the same node overwrites the previous head in memory, so that only the current state of the network is stored.
 
+HEADs message format :
+
+    {
+        name: "HEAD",
+        body: {
+            heads: [
+                HEAD_0,
+                HEAD_1,
+                ...
+            ]
+        }
+    }
+
 ### HEAD v0
 
 Accepted since duniter-ts **v1.6.0**