diff --git a/docker-compose.yml b/docker-compose.yml
index 7e4dbe0..4063285 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -40,6 +40,11 @@ services:
       # Application Configuration
       JWT_SECRET: ${JWT_SECRET}
       SERVER_PORT: 8765
+      # IMPORTANT: Device sync requires full URL with protocol
+      # Local: http://localhost:8765
+      # Local network: http://192.168.1.X:8765
+      # Domain: https://bookhoard.example.com
+      BASE_URL: http://localhost:${SERVER_PORT}
 
       # Rate Limiting Configuration
       TEST_MODE: ${TEST_MODE:-false}