diff --git a/src/PepperDash.Essentials.MobileControl/WebSocketServer/JoinResponse.cs b/src/PepperDash.Essentials.MobileControl/WebSocketServer/JoinResponse.cs
index 1529d0fe..7f2266a5 100644
--- a/src/PepperDash.Essentials.MobileControl/WebSocketServer/JoinResponse.cs
+++ b/src/PepperDash.Essentials.MobileControl/WebSocketServer/JoinResponse.cs
@@ -64,6 +64,12 @@ namespace PepperDash.Essentials.WebSocketServer
     [JsonProperty("userAppUrl")]
     public string UserAppUrl { get; set; }
 
+    /// <summary>
+    /// Gets or sets the WebSocketUrl with clientId query parameter
+    /// </summary>
+    [JsonProperty("webSocketUrl")]
+    public string WebSocketUrl { get; set; }
+
 
     /// <summary>
     /// Gets or sets the EnableDebug
diff --git a/src/PepperDash.Essentials.MobileControl/WebSocketServer/MobileControlWebsocketServer.cs b/src/PepperDash.Essentials.MobileControl/WebSocketServer/MobileControlWebsocketServer.cs
index 25cd7ba7..252d2814 100644
--- a/src/PepperDash.Essentials.MobileControl/WebSocketServer/MobileControlWebsocketServer.cs
+++ b/src/PepperDash.Essentials.MobileControl/WebSocketServer/MobileControlWebsocketServer.cs
@@ -68,6 +68,12 @@ namespace PepperDash.Essentials.WebSocketServer
         /// </summary>
         private readonly ConcurrentDictionary<string, string> pendingClientRegistrations = new ConcurrentDictionary<string, string>();
 
+        /// <summary>
+        /// Stores queues of pending client IDs per token for legacy clients (FIFO)
+        /// This ensures thread-safety when multiple legacy clients use the same token
+        /// </summary>
+        private readonly ConcurrentDictionary<string, ConcurrentQueue<string>> legacyClientIdQueues = new ConcurrentDictionary<string, ConcurrentQueue<string>>();
+
         /// <summary>
         /// Gets the collection of UI clients
         /// </summary>
@@ -730,49 +736,95 @@ namespace PepperDash.Essentials.WebSocketServer
 
         private UiClient BuildUiClient(string roomKey, JoinToken token, string key)
         {
-            // Try to retrieve a pending client ID that was registered during the join request
-            // Use the composite key: token-clientId
-            string clientId = null;
-            string registrationKey = null;
-            
-            // Find a registration for this token
-            var matchingRegistrations = pendingClientRegistrations.Keys
-                .Where(k => k.StartsWith($"{key}-"))
-                .OrderBy(k => k) // Process in order for FIFO behavior
-                .ToList();
-            
-            if (matchingRegistrations.Any())
+            // Dequeue the next clientId for legacy client support (FIFO per token)
+            // New clients will override this ID in OnOpen with the validated query parameter value
+            var clientId = "pending";
+            if (legacyClientIdQueues.TryGetValue(key, out var queue) && queue.TryDequeue(out var dequeuedId))
             {
-                registrationKey = matchingRegistrations.First();
-                if (pendingClientRegistrations.TryRemove(registrationKey, out clientId))
-                {
-                    this.LogVerbose("Retrieved pending clientId {clientId} for token {key}", clientId, key);
-                }
-            }
-            
-            if (clientId == null)
-            {
-                // Fallback: generate a new client ID if none was pending
-                clientId = $"{Utilities.GetNextClientId()}";
-                this.LogWarning("No pending clientId found for token {key}, generated new ID {clientId}", key, clientId);
+                clientId = dequeuedId;
+                this.LogVerbose("Dequeued legacy clientId {clientId} for token {token}", clientId, key);
             }
             
             var c = new UiClient($"uiclient-{key}-{roomKey}-{clientId}", clientId, token.Token, token.TouchpanelKey);
-            this.LogInformation("Constructing UiClient with key {key} and ID {id}", key, clientId);
+            this.LogInformation("Constructing UiClient with key {key} and temporary ID (will be set from query param)", key);
             c.Controller = _parent;
             c.RoomKey = roomKey;
             c.TokenKey = key; // Store the URL token key for filtering
+            c.Server = this; // Give UiClient access to server for ID registration
 
-            uiClients.AddOrUpdate(clientId, c, (id, existingClient) =>
+            // Don't add to uiClients yet - will be added in OnOpen after ID is set from query param
+            
+            c.ConnectionClosed += (o, a) => 
             {
-                this.LogWarning("replacing client with duplicate id {id}", id);
-                return c;
-            });
-            // UiClients[key].SetClient(c);
-            c.ConnectionClosed += (o, a) => uiClients.TryRemove(a.ClientId, out _);
+                uiClients.TryRemove(a.ClientId, out _);
+                // Clean up any pending registrations for this token
+                var keysToRemove = pendingClientRegistrations.Keys
+                    .Where(k => k.StartsWith($"{key}-"))
+                    .ToList();
+                foreach (var k in keysToRemove)
+                {
+                    pendingClientRegistrations.TryRemove(k, out _);
+                }
+                
+                // Clean up legacy queue if empty
+                if (legacyClientIdQueues.TryGetValue(key, out var legacyQueue) && legacyQueue.IsEmpty)
+                {
+                    legacyClientIdQueues.TryRemove(key, out _);
+                }
+            };
             return c;
         }
 
+        /// <summary>
+        /// Registers a UiClient with its validated client ID after WebSocket connection
+        /// </summary>
+        /// <param name="client">The UiClient to register</param>
+        /// <param name="clientId">The validated client ID</param>
+        /// <param name="tokenKey">The token key for validation</param>
+        /// <returns>True if registration successful, false if validation failed</returns>
+        public bool RegisterUiClient(UiClient client, string clientId, string tokenKey)
+        {
+            var registrationKey = $"{tokenKey}-{clientId}";
+            
+            // Verify this clientId was generated during a join request for this token
+            if (!pendingClientRegistrations.TryRemove(registrationKey, out _))
+            {
+                this.LogWarning("Client attempted to connect with unregistered or expired clientId {clientId} for token {token}", clientId, tokenKey);
+                return false;
+            }
+
+            // Registration is valid - add to active clients
+            uiClients.AddOrUpdate(clientId, client, (id, existingClient) =>
+            {
+                this.LogWarning("Replacing existing client with duplicate id {id}", id);
+                return client;
+            });
+            
+            this.LogInformation("Successfully registered UiClient with ID {clientId} for token {token}", clientId, tokenKey);
+            return true;
+        }
+
+        /// <summary>
+        /// Registers a UiClient using legacy flow (for backwards compatibility with older clients)
+        /// </summary>
+        /// <param name="client">The UiClient to register</param>
+        public void RegisterLegacyUiClient(UiClient client)
+        {
+            if (string.IsNullOrEmpty(client.Id))
+            {
+                this.LogError("Cannot register client with null or empty ID");
+                return;
+            }
+
+            uiClients.AddOrUpdate(client.Id, client, (id, existingClient) =>
+            {
+                this.LogWarning("Replacing existing client with duplicate id {id} (legacy flow)", id);
+                return client;
+            });
+            
+            this.LogInformation("Successfully registered UiClient with ID {clientId} using legacy flow", client.Id);
+        }
+
         /// <summary>
         /// Prints out the session data for each path
         /// </summary>
@@ -1079,15 +1131,23 @@ namespace PepperDash.Essentials.WebSocketServer
                 });
             }
 
-            // Generate a client ID for this join request and store it with a composite key
+            // Generate a client ID for this join request
             var clientId = $"{Utilities.GetNextClientId()}";
             
-            // Store registration with composite key: token-clientId so BuildUiClient can verify it
+            // Store in pending registrations for new clients that send clientId via query param
             var registrationKey = $"{token}-{clientId}";
             pendingClientRegistrations.TryAdd(registrationKey, clientId);
+            
+            // Also enqueue for legacy clients (thread-safe FIFO per token)
+            var queue = legacyClientIdQueues.GetOrAdd(token, _ => new ConcurrentQueue<string>());
+            queue.Enqueue(clientId);
 
             this.LogVerbose("Assigning ClientId: {clientId} for token: {token}", clientId, token);
 
+            // Construct WebSocket URL with clientId query parameter
+            var wsProtocol = "ws";
+            var wsUrl = $"{wsProtocol}://{CrestronEthernetHelper.GetEthernetParameter(CrestronEthernetHelper.ETHERNET_PARAMETER_TO_GET.GET_CURRENT_IP_ADDRESS, 0)}:{Port}{_wsPath}{token}?clientId={clientId}";
+
             // Construct the response object
             JoinResponse jRes = new JoinResponse
             {
@@ -1101,6 +1161,7 @@ namespace PepperDash.Essentials.WebSocketServer
                 UserAppUrl = string.Format("http://{0}:{1}/mc/app",
                 CrestronEthernetHelper.GetEthernetParameter(CrestronEthernetHelper.ETHERNET_PARAMETER_TO_GET.GET_CURRENT_IP_ADDRESS, 0),
                 Port),
+                WebSocketUrl = wsUrl,
                 EnableDebug = false,
                 DeviceInterfaceSupport = deviceInterfaces
             };
diff --git a/src/PepperDash.Essentials.MobileControl/WebSocketServer/UiClient.cs b/src/PepperDash.Essentials.MobileControl/WebSocketServer/UiClient.cs
index 61e5d042..fd012bbe 100644
--- a/src/PepperDash.Essentials.MobileControl/WebSocketServer/UiClient.cs
+++ b/src/PepperDash.Essentials.MobileControl/WebSocketServer/UiClient.cs
@@ -46,6 +46,11 @@ namespace PepperDash.Essentials.WebSocketServer
         /// </summary>
         public MobileControlSystemController Controller { get; set; }
 
+        /// <summary>
+        /// Gets or sets the server instance for client registration
+        /// </summary>
+        public MobileControlWebsocketServer Server { get; set; }
+
         /// <summary>
         /// Gets or sets the room key that this client is associated with
         /// </summary>
@@ -104,6 +109,50 @@ namespace PepperDash.Essentials.WebSocketServer
             Log.Output = (data, message) => Utilities.ConvertWebsocketLog(data, message, this);
             Log.Level = LogLevel.Trace;
 
+            // Get clientId from query parameter
+            var queryString = Context.QueryString;
+            var clientId = queryString["clientId"];
+
+            if (!string.IsNullOrEmpty(clientId))
+            {
+                // New behavior: Validate and register with the server using provided clientId
+                if (Server == null || !Server.RegisterUiClient(this, clientId, TokenKey))
+                {
+                    this.LogError("Failed to register client with ID {clientId}. Invalid or expired registration.", clientId);
+                    Context.WebSocket.Close(CloseStatusCode.PolicyViolation, "Invalid or expired clientId");
+                    return;
+                }
+
+                // Update this client's ID to the validated one
+                Id = clientId;
+                Key = $"uiclient-{TokenKey}-{RoomKey}-{clientId}";
+
+                this.LogInformation("Client {clientId} successfully connected and registered (new flow)", clientId);
+            }
+            else
+            {
+                // Legacy behavior: Use clientId from Token.Id (generated in HandleJoinRequest)
+                this.LogInformation("Client connected without clientId query parameter. Using legacy registration flow.");
+
+                // Id is already set from Token in constructor, use it
+                if (string.IsNullOrEmpty(Id))
+                {
+                    this.LogError("Legacy client has no ID from token. Connection will be closed.");
+                    Context.WebSocket.Close(CloseStatusCode.PolicyViolation, "No client ID available");
+                    return;
+                }
+
+                Key = $"uiclient-{TokenKey}-{RoomKey}-{Id}";
+
+                // Register directly to active clients (legacy flow)
+                if (Server != null)
+                {
+                    Server.RegisterLegacyUiClient(this);
+                }
+
+                this.LogInformation("Client {clientId} registered using legacy flow", Id);
+            }
+
             if (Controller == null)
             {
                 Debug.LogMessage(LogEventLevel.Verbose, "WebSocket UiClient Controller is null");