diff --git a/src/main/java/ch/unibas/dmi/dbis/cs108/casono/Main.java b/src/main/java/ch/unibas/dmi/dbis/cs108/casono/Main.java
index cbf1cc2..0c82c19 100644
--- a/src/main/java/ch/unibas/dmi/dbis/cs108/casono/Main.java
+++ b/src/main/java/ch/unibas/dmi/dbis/cs108/casono/Main.java
@@ -17,10 +17,13 @@ public final class Main {
             printUsage();
             System.exit(1);
         }
-
         switch (args[0]) {
             case "server" -> ServerApp.start(args[1]);
-            case "client" -> ClientApp.start(args[1]);
+            case "client" -> {
+                String address = args[1];
+                String username = args.length >= 3 ? args[2] : null;
+                ClientApp.start(address, username);
+            }
             default -> {
                 printUsage();
                 System.exit(1);
@@ -29,12 +32,13 @@ public final class Main {
     }
 
     private static boolean isValid(String[] args) {
-        if (args.length != 2) {
+        if (args.length < 2) {
             return false;
         }
 
         return switch (args[0]) {
-            case "server", "client" -> true;
+            case "server" -> args.length == 2;
+            case "client" -> args.length == 2 || args.length == 3;
             default -> false;
         };
     }
@@ -45,7 +49,7 @@ public final class Main {
                 """
                 Usage:
                   java -jar xyz.jar server <listenPort>
-                  java -jar xyz.jar client <serverIp>:<serverPort>
+                  java -jar xyz.jar client <serverIp>:<serverPort> [<username>]
                 """);
     }
 }
diff --git a/src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/ClientApp.java b/src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/ClientApp.java
index d5e2e2a..6b7267b 100644
--- a/src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/ClientApp.java
+++ b/src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/ClientApp.java
@@ -27,7 +27,7 @@ public class ClientApp {
      * @param arg Address in the format "ip:port".
      * @throws IllegalArgumentException if the address format is invalid.
      */
-    public static void start(String arg) {
+    public static void start(String arg, String username) {
         String[] parts = arg.split(":", 2);
         if (parts.length != 2) {
             throw new IllegalArgumentException("Address must be in format <ip>:<port>.");
@@ -36,6 +36,12 @@ public class ClientApp {
         int port = Integer.parseInt(parts[1]);
 
         LOGGER.info("You've selected the client. It will connect port {} at host {}", port, host);
+        // Pass connection defaults and optional username to the UI via system properties
+        System.setProperty("casono.server.host", host);
+        System.setProperty("casono.server.port", String.valueOf(port));
+        if (username != null && !username.isBlank()) {
+            System.setProperty("casono.username", username);
+        }
         Launcher.main(new String[] {});
     }
 }