diff --git a/docs/swarm/ui.md b/docs/swarm/ui.md
index 63d0bf0e..fe33f3cc 100644
--- a/docs/swarm/ui.md
+++ b/docs/swarm/ui.md
@@ -117,6 +117,10 @@ same whichever host runs each service:
 | Matrix   | `services.hyperhive.swarm.matrix.gatewayHost`     |
 | Bao      | `services.hyperhive.swarm.bao.ui.domain`          |
 
+Each entry is present whenever its option has a value — every option in
+the table defaults to one, so the link appears even on a swarm that runs
+no instance of that service.
+
 `nix/host-modules/swarm-controller.nix` builds these entries. `swarm-ui.nix`
 adds one more, for this UI's own API docs. An operator can add entries
 directly. An empty list hides the button.