diff --git a/docker-compose.yml b/docker-compose.yml
index 239bf8a..769a813 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -9,8 +9,12 @@ services:
       - ./public:/var/www/html/public
       - ./config.php:/var/www/html/config.php
 
+  # Relay is opt-in via the `relay` profile. Plain `docker compose up`
+  # starts just the app; use `docker compose --profile relay up` when
+  # you want to develop against a local relay instead of a remote one.
   relay:
     build: ./relay
+    profiles: ["relay"]
     ports:
       - "8081:80"
     volumes: