diff --git a/README.md b/README.md
index 1b638514..9419a254 100644
--- a/README.md
+++ b/README.md
@@ -116,6 +116,15 @@ lives at `/var/lib/nixos-containers/hive-matrix/`. Federation is
 enabled with an empty `trusted_servers` list; e2ee is deferred to
 a follow-up (#551).
 
+Optional: set `hyperhive.matrix.gui.enable = true;` to serve a
+[fluffychat-web](https://fluffychat.im) matrix client at `/matrix/`
+on the hive-c0re dashboard port. Disabled by default. The `◆ M4TR1X ◆ →`
+tab appears in the dashboard chrome when enabled. Override the client
+package with `hyperhive.matrix.gui.package = pkgs.cinny;` or any
+other `pkgs.*-web` static-dist derivation. Requires `hyperhive.matrix`
+(tuwunel) to be configured; the operator logs in to the web client
+by typing the homeserver URL at first visit.
+
 ## Agent configuration
 
 Per-agent settings live in each agent's `agent.nix` and are synced to