diff --git a/Server/src/main/java/uulm/teamname/marvelous/server/netconnector/MarvelousServer.java b/Server/src/main/java/uulm/teamname/marvelous/server/netconnector/MarvelousServer.java
index 5cb33c0..dfd72f3 100644
--- a/Server/src/main/java/uulm/teamname/marvelous/server/netconnector/MarvelousServer.java
+++ b/Server/src/main/java/uulm/teamname/marvelous/server/netconnector/MarvelousServer.java
@@ -12,32 +12,29 @@ public class MarvelousServer extends WebSocketServer {
     @Override
     public void onOpen(WebSocket conn, ClientHandshake handshake) {
         Logger.info("New client connected. Adding new User.");
-        userManager.connectUser(conn, handshake);
-        // TODO: Send messages to UserManager, which then packages that stuff and sends it further
+        userManager.connectUser(conn);
     }
 
     @Override
     public void onClose(WebSocket conn, int code, String reason, boolean remote) {
         Logger.info("Client disconnected");
         userManager.disconnectUser(conn, remote);
-        // TODO: Send messages to UserManager, which then removes the user and such
     }
 
     @Override
     public void onMessage(WebSocket conn, String message) {
         Logger.debug("Message received: {}", message);
         userManager.messageReceived(conn, message);
-        // TODO: Send messages to UserManager, which then packages them and sends them further
     }
 
     @Override
     public void onError(WebSocket conn, Exception ex) {
-        // TODO: Send errors to UserManager, which then answers with even more errors
+        Logger.warn("WebSocket-Error occurred: {}", ex.getMessage());
     }
 
     @Override
     public void onStart() {
-        // TODO: Get the UserManager, and tell it that this thing is active
+        Logger.info("MarvelousServer started on Address {}", this.getAddress().toString());
     }
 
     private final UserManager userManager;
diff --git a/Server/src/main/java/uulm/teamname/marvelous/server/netconnector/UserManager.java b/Server/src/main/java/uulm/teamname/marvelous/server/netconnector/UserManager.java
index b4f63e8..c71acf1 100644
--- a/Server/src/main/java/uulm/teamname/marvelous/server/netconnector/UserManager.java
+++ b/Server/src/main/java/uulm/teamname/marvelous/server/netconnector/UserManager.java
@@ -1,9 +1,8 @@
 package uulm.teamname.marvelous.server.netconnector;
 
-import org.java_websocket.handshake.ClientHandshake;
 import org.tinylog.Logger;
 import uulm.teamname.marvelous.gamelibrary.json.JSON;
-import uulm.teamname.marvelous.gamelibrary.messages.BasicMessage;
+import uulm.teamname.marvelous.gamelibrary.json.ValidationUtility;
 import uulm.teamname.marvelous.gamelibrary.messages.ErrorMessage;
 import uulm.teamname.marvelous.gamelibrary.messages.client.*;
 import uulm.teamname.marvelous.server.lobbymanager.Participant;
@@ -12,13 +11,17 @@ import org.java_websocket.WebSocket;
 
 import java.util.*;
 
+/** Class that manages users. It is meant as an extension to the {@link MarvelousServer} class, and should not be called
+ * from anywhere else. This is the first place where messages are relayed to after they get received. This class is
+ * responsible for handshakes, reconnects and WebSocket-to-Participant matching. <b>It is not thread-safe.</b>
+ */
 public class UserManager {
 
     /** A set of users that aren't assigned to lobbies or character selection yet */
     private final HashSet<WebSocket> newUsers;
 
     /** A set of users that can reconnect if they wish to do so, and their matching Participants */
-    private final HashMap<WebSocket, Participant> readyToReconnect;
+    private final HashMap<WebSocket, SUID> readyToReconnect;
 
     /** A set of users that only have to send the
      * {@link uulm.teamname.marvelous.gamelibrary.messages.client.PlayerReadyMessage} to be assigned
@@ -49,24 +52,51 @@ public class UserManager {
     }
 
     /** Called on a new WebSocket connection. Places the WebSocket and its ResourceDescriptor in a HashMap. */
-    public void connectUser(WebSocket conn, ClientHandshake handshake) {
-        synchronized (newUsers) {
-            newUsers.add(conn);
-        }
+    public void connectUser(WebSocket conn) {
+        newUsers.add(conn);
     }
 
+    /**
+     * Called on any received messages. The method checks the message for validity, and then relays it
+     * accordingly. {@link HelloServerMessage HelloServerMessages} and {@link ReconnectMessage ReconnectMessages}
+     * are handled in this component, whereby a handshake or reconnect is performed, respectively.
+     * @param conn is the {@link WebSocket} that sent the message
+     * @param message is the {@link String} sent by the connection
+     */
     public void messageReceived(WebSocket conn, String message) {
-        // TODO: Implement more than only a basic handshake
-
+        Logger.trace("Parsing message...");
         var parsedMessageOptional = json.parse(message);
         if (parsedMessageOptional.isEmpty()) {
-            Logger.debug("Invalid message '{}' received, sending error", message);
+            Logger.debug("Message '{}' was invalid, sending error", message);
             sendError(conn, "Message could not be parsed");
         } else {
             var parsedMessage = parsedMessageOptional.get();
 
-            if (parsedMessage instanceof HelloServerMessage)
-                 handshake(conn, (HelloServerMessage) parsedMessage);
+            Logger.trace("Validating message...");
+            var violations = ValidationUtility.validate(parsedMessage);
+
+            if (violations.isPresent()) {
+                Logger.debug("Message '{}' was invalid: {}, sending error", message, violations.get());
+                sendError(conn, violations.get());
+            } else {
+                Logger.trace("Message was valid. Checking type of message...");
+
+                if (parsedMessage instanceof HelloServerMessage) {
+                    Logger.trace("Message is instanceof HelloServerMessage, initiating handshake");
+                    handshake(conn, (HelloServerMessage) parsedMessage);
+                } else if (parsedMessage instanceof ReconnectMessage) {
+                    Logger.trace("Message is instanceof ReconnectMessage, initiating reconnect");
+                    reconnectClient(conn, (ReconnectMessage) parsedMessage);
+                } else if (parsedMessage instanceof PlayerReadyMessage) {
+                    Logger.trace("Message is instanceof PlayerReadyMessage, assigning lobby");
+                    assignLobby(conn, (PlayerReadyMessage) parsedMessage);
+                } else {
+                    Logger.debug("Message '{}' has invalid type, Error will be sent");
+                    sendError(conn, String.format(
+                            "Message '%s' has invalid type, and cannot be processed on the server",
+                            message));
+                }
+            }
         }
     }
 
@@ -85,7 +115,7 @@ public class UserManager {
         var participant = activeParticipants.get(clientID);
         if (participant != null) {
             synchronized (readyToReconnect) {
-                readyToReconnect.put(conn, participant);
+                readyToReconnect.put(conn, clientID);
             }
         } else {
             Logger.trace("removing handshaking user from newUsers");
@@ -99,33 +129,37 @@ public class UserManager {
         }
     }
 
-    public void reconnectClient(WebSocket conn, ReconnectMessage message) {
-        if (!readyToConnect.containsKey(conn)) {
+    void reconnectClient(WebSocket conn, ReconnectMessage message) {
+        if (!readyToReconnect.containsKey(conn)) {
             Logger.debug("Non-reconnect-allowed client has sent reconnect message, sending error");
             sendError(conn, "Reconnect is not possible");
-            return;
-        }
-        Logger.info("Reconnecting client {} to their lobby");
-        var participantToRestore = readyToReconnect.get(conn);
-        synchronized (participantToRestore) {
+        } else if (message.reconnect) {
+            Logger.info("Reconnecting client {} to their lobby", conn);
+            var clientID = readyToReconnect.get(conn);
+            var participantToRestore = activeParticipants.get(clientID);
+
             participantToRestore.setConnection(conn);
-        }
-        synchronized (readyToReconnect) {
+            readyToReconnect.remove(conn);
+            inGame.put(conn, participantToRestore);
+            // activeParticipants remains the same, as no players have been removed from the game
+        } else {
+            Logger.debug(
+                    "Client {} refused reconnection, will therefore be put into readyToConnect clients",
+                    conn);
+
+            var clientID = readyToReconnect.get(conn);
+            readyToConnect.put(conn, clientID);
             readyToReconnect.remove(conn);
         }
-        synchronized (inGame) {
-            inGame.put(conn, participantToRestore);
-        }
-        // activeParticipants remains the same, as no players have been removed from the game
     }
 
-    public void assignLobby(WebSocket conn, PlayerReadyMessage message) {
+    void assignLobby(WebSocket conn, PlayerReadyMessage message) {
     }
 
-    public void charactersSelected(WebSocket conn, CharacterSelectionMessage message) {
+    void charactersSelected(WebSocket conn, CharacterSelectionMessage message) {
     }
 
-    public void relayRequestMessage(Participant conn, RequestMessage message) {
+    void relayRequestMessage(Participant conn, RequestMessage message) {
     }
 
     /** Sends an {@link uulm.teamname.marvelous.gamelibrary.messages.ErrorMessage} to the specified user. */
@@ -158,26 +192,31 @@ public class UserManager {
     }
 
     /** Package-private getter for mutable newUsers HashSet, meant for testing */
+    @Deprecated
     HashSet<WebSocket> getNewUsers() {
         return newUsers;
     }
 
     /** Package-private getter for mutable readyToReconnect HashMap, meant for testing */
-    HashMap<WebSocket, Participant> getReadyToReconnect() {
+    @Deprecated
+    HashMap<WebSocket, SUID> getReadyToReconnect() {
         return readyToReconnect;
     }
 
     /** Package-private getter for mutable readyToConnect HashMap, meant for testing */
+    @Deprecated
     HashMap<WebSocket, SUID> getReadyToConnect() {
         return readyToConnect;
     }
 
     /** Package-private getter for mutable inGame HashMap, meant for testing */
+    @Deprecated
     HashMap<WebSocket, Participant> getInGame() {
         return inGame;
     }
 
     /** Package-private getter for mutable activeParticipants HashMap, meant for testing */
+    @Deprecated
     HashMap<SUID, Participant> getActiveParticipants() {
         return activeParticipants;
     }