diff --git a/doc/9p.md b/doc/9p.md
index 6ad7867..b32608b 100644
--- a/doc/9p.md
+++ b/doc/9p.md
@@ -248,20 +248,25 @@ output here
 
 ---
 
-## Authentication
+## Authentication and permissions
 
-olliesrv does not require authentication — any client that can reach the Unix
-socket (or TCP port) can connect.
+Both servers use the identity provided at attach time for permission enforcement.
 
-toolsrv requires Tauth. The protocol:
+**olliesrv** does not require Tauth (no secret exchange), but the `uname` from
+Tattach is used for standard 9P file permission checks (uid/gid/world bits).
+Files are owned by the server's user with group `agent`; any attaching client
+is added to the `agent` group, so group permission bits govern what agents can
+access.
 
-1. Client sends Tauth with a shared secret as the write payload and `aname`
-   identifying the agent.
-2. Server verifies the secret (first client sets it; subsequent clients must match).
-3. Server returns a session token via read on the auth fid.
-4. Client attaches using the authenticated afid.
+**toolsrv** requires Tauth. The protocol:
 
-The `aname` field is used for permission enforcement — it scopes tool registry
-lookups and process ownership to the connecting agent. Currently there is no
-mechanism to prevent one agent from claiming another's identity; the scheme
-relies on all clients being spawned by olliesrv with the correct secret.
+1. Client sends Tauth with `aname` identifying the agent.
+2. Client writes the shared secret to the auth fid.
+3. Server verifies the secret (first client sets it; subsequent clients must match).
+4. Server returns a session token via read on the auth fid.
+5. Client attaches using the authenticated afid.
+
+The `aname` field scopes tool registry lookups and process ownership to the
+connecting agent. Currently there is no mechanism to prevent one agent from
+claiming another's identity; the scheme relies on all clients being spawned by
+olliesrv with the correct secret.