Phase 0 — mechanical rename ZB.MOM.WW.LmxOpcUa.* → ZB.MOM.WW.OtOpcUa.*

Renames all 11 projects (5 src + 6 tests), the .slnx solution file, all source-file namespaces, all axaml namespace references, and all v1 documentation references in CLAUDE.md and docs/*.md (excluding docs/v2/ which is already in OtOpcUa form). Also updates the TopShelf service registration name from "LmxOpcUa" to "OtOpcUa" per Phase 0 Task 0.6. Preserves runtime identifiers per Phase 0 Out-of-Scope rules to avoid breaking v1/v2 client trust during coexistence: OPC UA `ApplicationUri` defaults (`urn:{GalaxyName}:LmxOpcUa`), server `EndpointPath` (`/LmxOpcUa`), `ServerName` default (feeds cert subject CN), `MxAccessConfiguration.ClientName` default (defensive — stays "LmxOpcUa" for MxAccess audit-trail consistency), client OPC UA identifiers (`ApplicationName = "LmxOpcUaClient"`, `ApplicationUri = "urn:localhost:LmxOpcUaClient"`, cert directory `%LocalAppData%\LmxOpcUaClient\pki\`), and the `LmxOpcUaServer` class name (class rename out of Phase 0 scope per Task 0.5 sed pattern; happens in Phase 1 alongside `LmxNodeManager → GenericDriverNodeManager` Core extraction). 23 LmxOpcUa references retained, all enumerated and justified in `docs/v2/implementation/exit-gate-phase-0.md`. Build clean: 0 errors, 30 warnings (lower than baseline 167). Tests at strict improvement over baseline: 821 passing / 1 failing vs baseline 820 / 2 (one flaky pre-existing failure passed this run; the other still fails — both pre-existing and unrelated to the rename). `Client.UI.Tests`, `Historian.Aveva.Tests`, `Client.Shared.Tests`, `IntegrationTests` all match baseline exactly. Exit gate compliance results recorded in `docs/v2/implementation/exit-gate-phase-0.md` with all 7 checks PASS or DEFERRED-to-PR-review (#7 service install verification needs Windows service permissions on the reviewer's box). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
2026-04-17 13:57:47 -04:00
parent 5b8d708c58
commit 3b2defd94f
293 changed files with 841 additions and 722 deletions
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/App.axaml
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/App.axaml
@@ -0,0 +1,9 @@
+<Application xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.App"
+             RequestedThemeVariant="Light">
+    <Application.Styles>
+        <FluentTheme />
+        <StyleInclude Source="avares://Avalonia.Controls.DataGrid/Themes/Fluent.xaml" />
+    </Application.Styles>
+</Application>
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/App.axaml.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/App.axaml.cs
@@ -0,0 +1,33 @@
+using Avalonia;
+using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Markup.Xaml;
+using ZB.MOM.WW.OtOpcUa.Client.Shared;
+using ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+using ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+using ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI;
+
+public class App : Application
+{
+    public override void Initialize()
+    {
+        AvaloniaXamlLoader.Load(this);
+    }
+
+    public override void OnFrameworkInitializationCompleted()
+    {
+        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
+        {
+            var factory = new OpcUaClientServiceFactory();
+            var dispatcher = new AvaloniaUiDispatcher();
+            var viewModel = new MainWindowViewModel(factory, dispatcher);
+            desktop.MainWindow = new MainWindow
+            {
+                DataContext = viewModel
+            };
+        }
+
+        base.OnFrameworkInitializationCompleted();
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Assets/app-icon.svg
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Assets/app-icon.svg
@@ -0,0 +1,18 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64" width="64" height="64">
+  <!-- Server/network icon for OPC UA -->
+  <rect x="8" y="6" width="48" height="36" rx="4" fill="#2563eb" stroke="#1d4ed8" stroke-width="2"/>
+  <rect x="14" y="12" width="36" height="24" rx="2" fill="#dbeafe"/>
+  <!-- Network nodes -->
+  <circle cx="24" cy="24" r="4" fill="#2563eb"/>
+  <circle cx="40" cy="20" r="3" fill="#3b82f6"/>
+  <circle cx="36" cy="30" r="3" fill="#3b82f6"/>
+  <!-- Connection lines -->
+  <line x1="24" y1="24" x2="40" y2="20" stroke="#60a5fa" stroke-width="1.5"/>
+  <line x1="24" y1="24" x2="36" y2="30" stroke="#60a5fa" stroke-width="1.5"/>
+  <line x1="40" y1="20" x2="36" y2="30" stroke="#60a5fa" stroke-width="1.5"/>
+  <!-- Base stand -->
+  <rect x="24" y="42" width="16" height="4" rx="1" fill="#6b7280"/>
+  <rect x="20" y="46" width="24" height="4" rx="2" fill="#9ca3af"/>
+  <!-- UA text -->
+  <text x="32" y="60" text-anchor="middle" font-family="Arial,sans-serif" font-size="8" font-weight="bold" fill="#1d4ed8">UA</text>
+</svg>
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Controls/DateTimeRangePicker.axaml
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Controls/DateTimeRangePicker.axaml
@@ -0,0 +1,27 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Controls.DateTimeRangePicker">
+    <StackPanel Orientation="Horizontal" Spacing="8">
+        <StackPanel Spacing="2">
+            <TextBlock Text="Start (UTC)" FontSize="11" Foreground="Gray" />
+            <TextBox Name="StartInput" Width="170" FontFamily="Consolas,monospace" FontSize="13"
+                     Watermark="yyyy-MM-dd HH:mm:ss (UTC)"
+                     Text="{Binding StartText, RelativeSource={RelativeSource AncestorType=UserControl}}" />
+        </StackPanel>
+        <TextBlock Text="to" VerticalAlignment="Bottom" Margin="0,0,0,6" />
+        <StackPanel Spacing="2">
+            <TextBlock Text="End (UTC)" FontSize="11" Foreground="Gray" />
+            <TextBox Name="EndInput" Width="170" FontFamily="Consolas,monospace" FontSize="13"
+                     Watermark="yyyy-MM-dd HH:mm:ss (UTC)"
+                     Text="{Binding EndText, RelativeSource={RelativeSource AncestorType=UserControl}}" />
+        </StackPanel>
+        <Border Background="#F0F0F0" CornerRadius="4" Padding="4,2" VerticalAlignment="Bottom" Margin="0,0,0,2">
+            <StackPanel Orientation="Horizontal" Spacing="4">
+                <Button Name="Last5MinBtn" Content="5m" Padding="8,3" FontSize="11" />
+                <Button Name="LastHourBtn" Content="1h" Padding="8,3" FontSize="11" />
+                <Button Name="LastDayBtn" Content="1d" Padding="8,3" FontSize="11" />
+                <Button Name="LastWeekBtn" Content="1w" Padding="8,3" FontSize="11" />
+            </StackPanel>
+        </Border>
+    </StackPanel>
+</UserControl>
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Controls/DateTimeRangePicker.axaml.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Controls/DateTimeRangePicker.axaml.cs
@@ -0,0 +1,187 @@
+using System;
+using System.Globalization;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Media;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Controls;
+
+/// <summary>
+/// A date/time range picker using formatted text boxes and preset duration buttons.
+/// Text properties are two-way bound to TextBoxes via XAML; DateTime properties
+/// are synced in code-behind.
+/// </summary>
+public partial class DateTimeRangePicker : UserControl
+{
+    private const string Format = "yyyy-MM-dd HH:mm:ss";
+
+    public static readonly StyledProperty<DateTimeOffset?> StartDateTimeProperty =
+        AvaloniaProperty.Register<DateTimeRangePicker, DateTimeOffset?>(
+            nameof(StartDateTime), defaultBindingMode: Avalonia.Data.BindingMode.TwoWay);
+
+    public static readonly StyledProperty<DateTimeOffset?> EndDateTimeProperty =
+        AvaloniaProperty.Register<DateTimeRangePicker, DateTimeOffset?>(
+            nameof(EndDateTime), defaultBindingMode: Avalonia.Data.BindingMode.TwoWay);
+
+    public static readonly StyledProperty<string> StartTextProperty =
+        AvaloniaProperty.Register<DateTimeRangePicker, string>(nameof(StartText), defaultValue: "");
+
+    public static readonly StyledProperty<string> EndTextProperty =
+        AvaloniaProperty.Register<DateTimeRangePicker, string>(nameof(EndText), defaultValue: "");
+
+    public static readonly StyledProperty<DateTimeOffset?> MinDateTimeProperty =
+        AvaloniaProperty.Register<DateTimeRangePicker, DateTimeOffset?>(nameof(MinDateTime));
+
+    public static readonly StyledProperty<DateTimeOffset?> MaxDateTimeProperty =
+        AvaloniaProperty.Register<DateTimeRangePicker, DateTimeOffset?>(nameof(MaxDateTime));
+
+    private bool _isUpdating;
+
+    public DateTimeRangePicker()
+    {
+        InitializeComponent();
+    }
+
+    public DateTimeOffset? StartDateTime
+    {
+        get => GetValue(StartDateTimeProperty);
+        set => SetValue(StartDateTimeProperty, value);
+    }
+
+    public DateTimeOffset? EndDateTime
+    {
+        get => GetValue(EndDateTimeProperty);
+        set => SetValue(EndDateTimeProperty, value);
+    }
+
+    public string StartText
+    {
+        get => GetValue(StartTextProperty);
+        set => SetValue(StartTextProperty, value);
+    }
+
+    public string EndText
+    {
+        get => GetValue(EndTextProperty);
+        set => SetValue(EndTextProperty, value);
+    }
+
+    public DateTimeOffset? MinDateTime
+    {
+        get => GetValue(MinDateTimeProperty);
+        set => SetValue(MinDateTimeProperty, value);
+    }
+
+    public DateTimeOffset? MaxDateTime
+    {
+        get => GetValue(MaxDateTimeProperty);
+        set => SetValue(MaxDateTimeProperty, value);
+    }
+
+    protected override void OnLoaded(RoutedEventArgs e)
+    {
+        base.OnLoaded(e);
+
+        var startInput = this.FindControl<TextBox>("StartInput");
+        var endInput = this.FindControl<TextBox>("EndInput");
+
+        if (startInput != null) startInput.LostFocus += OnStartLostFocus;
+        if (endInput != null) endInput.LostFocus += OnEndLostFocus;
+
+        var last5Min = this.FindControl<Button>("Last5MinBtn");
+        var lastHour = this.FindControl<Button>("LastHourBtn");
+        var lastDay = this.FindControl<Button>("LastDayBtn");
+        var lastWeek = this.FindControl<Button>("LastWeekBtn");
+
+        if (last5Min != null) last5Min.Click += (_, _) => ApplyPreset(TimeSpan.FromMinutes(5));
+        if (lastHour != null) lastHour.Click += (_, _) => ApplyPreset(TimeSpan.FromHours(1));
+        if (lastDay != null) lastDay.Click += (_, _) => ApplyPreset(TimeSpan.FromDays(1));
+        if (lastWeek != null) lastWeek.Click += (_, _) => ApplyPreset(TimeSpan.FromDays(7));
+    }
+
+    protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
+    {
+        base.OnPropertyChanged(change);
+        if (_isUpdating) return;
+
+        if (change.Property == StartDateTimeProperty)
+        {
+            _isUpdating = true;
+            StartText = StartDateTime?.UtcDateTime.ToString(Format) ?? "";
+            _isUpdating = false;
+        }
+        else if (change.Property == EndDateTimeProperty)
+        {
+            _isUpdating = true;
+            EndText = EndDateTime?.UtcDateTime.ToString(Format) ?? "";
+            _isUpdating = false;
+        }
+    }
+
+    private void OnStartLostFocus(object? sender, RoutedEventArgs e)
+    {
+        var startInput = this.FindControl<TextBox>("StartInput");
+        if (startInput == null) return;
+
+        if (TryParseDateTime(startInput.Text, out var dt))
+        {
+            _isUpdating = true;
+            StartDateTime = dt;
+            _isUpdating = false;
+            startInput.Foreground = null;
+        }
+        else if (!string.IsNullOrWhiteSpace(startInput.Text))
+        {
+            startInput.Foreground = Brushes.Red;
+        }
+    }
+
+    private void OnEndLostFocus(object? sender, RoutedEventArgs e)
+    {
+        var endInput = this.FindControl<TextBox>("EndInput");
+        if (endInput == null) return;
+
+        if (TryParseDateTime(endInput.Text, out var dt))
+        {
+            _isUpdating = true;
+            EndDateTime = dt;
+            _isUpdating = false;
+            endInput.Foreground = null;
+        }
+        else if (!string.IsNullOrWhiteSpace(endInput.Text))
+        {
+            endInput.Foreground = Brushes.Red;
+        }
+    }
+
+    private void ApplyPreset(TimeSpan span)
+    {
+        _isUpdating = true;
+        try
+        {
+            var now = DateTimeOffset.UtcNow;
+            StartDateTime = now - span;
+            EndDateTime = now;
+            StartText = StartDateTime.Value.UtcDateTime.ToString(Format);
+            EndText = EndDateTime.Value.UtcDateTime.ToString(Format);
+        }
+        finally
+        {
+            _isUpdating = false;
+        }
+    }
+
+    private static bool TryParseDateTime(string? text, out DateTimeOffset result)
+    {
+        result = default;
+        if (string.IsNullOrWhiteSpace(text)) return false;
+
+        if (DateTimeOffset.TryParseExact(text, Format, CultureInfo.InvariantCulture,
+                DateTimeStyles.AssumeUniversal, out result))
+            return true;
+
+        return DateTimeOffset.TryParse(text, CultureInfo.InvariantCulture,
+            DateTimeStyles.AssumeUniversal, out result);
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Helpers/StatusCodeFormatter.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Helpers/StatusCodeFormatter.cs
@@ -0,0 +1,36 @@
+using Opc.Ua;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Helpers;
+
+/// <summary>
+/// Formats OPC UA status codes as "0xHEX (description)".
+/// </summary>
+internal static class StatusCodeFormatter
+{
+    public static string Format(StatusCode statusCode)
+    {
+        var code = statusCode.Code;
+        var hex = $"0x{code:X8}";
+
+        // Try the SDK's browse name lookup first
+        var name = StatusCodes.GetBrowseName(code);
+        if (!string.IsNullOrEmpty(name))
+            return $"{hex} ({name})";
+
+        // Try masking to just the main code (top 16 bits) for sub-status codes
+        var mainCode = code & 0xFFFF0000;
+        if (mainCode != code)
+        {
+            name = StatusCodes.GetBrowseName(mainCode);
+            if (!string.IsNullOrEmpty(name))
+                return $"{hex} ({name})";
+        }
+
+        // Fallback to severity category
+        if (StatusCode.IsGood(statusCode))
+            return $"{hex} (Good)";
+        if (StatusCode.IsBad(statusCode))
+            return $"{hex} (Bad)";
+        return $"{hex} (Uncertain)";
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Helpers/ValueFormatter.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Helpers/ValueFormatter.cs
@@ -0,0 +1,33 @@
+using System.Collections;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Helpers;
+
+/// <summary>
+/// Formats OPC UA values for display, with array support.
+/// </summary>
+internal static class ValueFormatter
+{
+    public static string Format(object? value)
+    {
+        if (value is null) return "(null)";
+        if (value is Array array) return FormatArray(array);
+        if (value is IEnumerable enumerable and not string) return FormatEnumerable(enumerable);
+        return value.ToString() ?? "(null)";
+    }
+
+    private static string FormatArray(Array array)
+    {
+        var elements = new string[array.Length];
+        for (var i = 0; i < array.Length; i++)
+            elements[i] = array.GetValue(i)?.ToString() ?? "null";
+        return $"[{string.Join(",", elements)}]";
+    }
+
+    private static string FormatEnumerable(IEnumerable enumerable)
+    {
+        var items = new List<string>();
+        foreach (var item in enumerable)
+            items.Add(item?.ToString() ?? "null");
+        return $"[{string.Join(",", items)}]";
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Program.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Program.cs
@@ -0,0 +1,21 @@
+using Avalonia;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI;
+
+public class Program
+{
+    [STAThread]
+    public static void Main(string[] args)
+    {
+        BuildAvaloniaApp()
+            .StartWithClassicDesktopLifetime(args);
+    }
+
+    public static AppBuilder BuildAvaloniaApp()
+    {
+        return AppBuilder.Configure<App>()
+            .UsePlatformDetect()
+            .WithInterFont()
+            .LogToTrace();
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Services/AvaloniaUiDispatcher.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Services/AvaloniaUiDispatcher.cs
@@ -0,0 +1,14 @@
+using Avalonia.Threading;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+/// <summary>
+///     Dispatches actions to the Avalonia UI thread.
+/// </summary>
+public sealed class AvaloniaUiDispatcher : IUiDispatcher
+{
+    public void Post(Action action)
+    {
+        Dispatcher.UIThread.Post(action);
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Services/ISettingsService.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Services/ISettingsService.cs
@@ -0,0 +1,10 @@
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+/// <summary>
+/// Loads and saves user settings.
+/// </summary>
+public interface ISettingsService
+{
+    UserSettings Load();
+    void Save(UserSettings settings);
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Services/IUiDispatcher.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Services/IUiDispatcher.cs
@@ -0,0 +1,12 @@
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+/// <summary>
+///     Abstraction for dispatching actions to the UI thread.
+/// </summary>
+public interface IUiDispatcher
+{
+    /// <summary>
+    ///     Posts an action to be executed on the UI thread.
+    /// </summary>
+    void Post(Action action);
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Services/JsonSettingsService.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Services/JsonSettingsService.cs
@@ -0,0 +1,50 @@
+using System.Text.Json;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+/// <summary>
+/// Persists user settings to a JSON file under LocalApplicationData.
+/// </summary>
+public sealed class JsonSettingsService : ISettingsService
+{
+    private static readonly string SettingsDir = Path.Combine(
+        Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+        "LmxOpcUaClient");
+
+    private static readonly string SettingsPath = Path.Combine(SettingsDir, "settings.json");
+
+    private static readonly JsonSerializerOptions JsonOptions = new()
+    {
+        WriteIndented = true
+    };
+
+    public UserSettings Load()
+    {
+        try
+        {
+            if (!File.Exists(SettingsPath))
+                return new UserSettings();
+
+            var json = File.ReadAllText(SettingsPath);
+            return JsonSerializer.Deserialize<UserSettings>(json, JsonOptions) ?? new UserSettings();
+        }
+        catch
+        {
+            return new UserSettings();
+        }
+    }
+
+    public void Save(UserSettings settings)
+    {
+        try
+        {
+            Directory.CreateDirectory(SettingsDir);
+            var json = JsonSerializer.Serialize(settings, JsonOptions);
+            File.WriteAllText(SettingsPath, json);
+        }
+        catch
+        {
+            // Best-effort save; don't crash the app
+        }
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Services/SynchronousUiDispatcher.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Services/SynchronousUiDispatcher.cs
@@ -0,0 +1,13 @@
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+/// <summary>
+///     Dispatcher that executes actions synchronously on the calling thread.
+///     Used for unit testing where no UI thread is available.
+/// </summary>
+public sealed class SynchronousUiDispatcher : IUiDispatcher
+{
+    public void Post(Action action)
+    {
+        action();
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Services/UserSettings.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Services/UserSettings.cs
@@ -0,0 +1,59 @@
+using ZB.MOM.WW.OtOpcUa.Client.Shared.Models;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+/// <summary>
+/// Persisted user connection settings.
+/// </summary>
+public sealed class UserSettings
+{
+    /// <summary>
+    /// Gets or sets the last OPC UA endpoint URL entered by the user.
+    /// </summary>
+    public string EndpointUrl { get; set; } = "opc.tcp://localhost:4840";
+
+    /// <summary>
+    /// Gets or sets the persisted username for authenticated sessions.
+    /// </summary>
+    public string? Username { get; set; }
+
+    /// <summary>
+    /// Gets or sets the persisted password for authenticated sessions.
+    /// </summary>
+    public string? Password { get; set; }
+
+    /// <summary>
+    /// Gets or sets the transport security mode selected by the user.
+    /// </summary>
+    public SecurityMode SecurityMode { get; set; } = SecurityMode.None;
+
+    /// <summary>
+    /// Gets or sets the raw failover endpoint list entered in the UI.
+    /// </summary>
+    public string? FailoverUrls { get; set; }
+
+    /// <summary>
+    /// Gets or sets the persisted session timeout, in seconds, for new client connections.
+    /// </summary>
+    public int SessionTimeoutSeconds { get; set; } = 60;
+
+    /// <summary>
+    /// Gets or sets a value indicating whether untrusted server certificates should be auto-accepted.
+    /// </summary>
+    public bool AutoAcceptCertificates { get; set; } = true;
+
+    /// <summary>
+    /// Gets or sets the certificate store path used for client certificates and trust lists.
+    /// </summary>
+    public string? CertificateStorePath { get; set; }
+
+    /// <summary>
+    /// Gets or sets the node IDs that should be re-subscribed when the UI reconnects.
+    /// </summary>
+    public List<string> SubscribedNodes { get; set; } = [];
+
+    /// <summary>
+    /// Gets or sets the alarm source node that should be restored when the UI reconnects.
+    /// </summary>
+    public string? AlarmSourceNodeId { get; set; }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/AlarmEventViewModel.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/AlarmEventViewModel.cs
@@ -0,0 +1,99 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+/// <summary>
+///     Represents a single alarm event row.
+/// </summary>
+public class AlarmEventViewModel : ObservableObject
+{
+    /// <summary>
+    /// Creates an alarm row model from an OPC UA condition event so the alarms tab can display and acknowledge it.
+    /// </summary>
+    /// <param name="sourceName">The source object or variable name associated with the alarm.</param>
+    /// <param name="conditionName">The OPC UA condition name reported by the server.</param>
+    /// <param name="severity">The alarm severity value presented to the operator.</param>
+    /// <param name="message">The alarm message text shown in the UI.</param>
+    /// <param name="retain">Indicates whether the server is retaining the alarm condition.</param>
+    /// <param name="activeState">Indicates whether the alarm is currently active.</param>
+    /// <param name="ackedState">Indicates whether the alarm has already been acknowledged.</param>
+    /// <param name="time">The event timestamp associated with the alarm state.</param>
+    /// <param name="eventId">The OPC UA event identifier used for acknowledgment calls.</param>
+    /// <param name="conditionNodeId">The condition node identifier used when acknowledging the alarm.</param>
+    public AlarmEventViewModel(
+        string sourceName,
+        string conditionName,
+        ushort severity,
+        string message,
+        bool retain,
+        bool activeState,
+        bool ackedState,
+        DateTime time,
+        byte[]? eventId = null,
+        string? conditionNodeId = null)
+    {
+        SourceName = sourceName;
+        ConditionName = conditionName;
+        Severity = severity;
+        Message = message;
+        Retain = retain;
+        ActiveState = activeState;
+        AckedState = ackedState;
+        Time = time;
+        EventId = eventId;
+        ConditionNodeId = conditionNodeId;
+    }
+
+    /// <summary>
+    /// Gets the source object or variable name associated with the alarm.
+    /// </summary>
+    public string SourceName { get; }
+
+    /// <summary>
+    /// Gets the OPC UA condition name reported for the alarm event.
+    /// </summary>
+    public string ConditionName { get; }
+
+    /// <summary>
+    /// Gets the severity value shown to the operator.
+    /// </summary>
+    public ushort Severity { get; }
+
+    /// <summary>
+    /// Gets the alarm message text shown in the UI.
+    /// </summary>
+    public string Message { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the server is retaining the condition.
+    /// </summary>
+    public bool Retain { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the alarm is currently active.
+    /// </summary>
+    public bool ActiveState { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the alarm has already been acknowledged.
+    /// </summary>
+    public bool AckedState { get; }
+
+    /// <summary>
+    /// Gets the event timestamp displayed for the alarm row.
+    /// </summary>
+    public DateTime Time { get; }
+
+    /// <summary>
+    /// Gets the OPC UA event identifier needed to acknowledge the alarm.
+    /// </summary>
+    public byte[]? EventId { get; }
+
+    /// <summary>
+    /// Gets the condition node identifier used for acknowledgment method calls.
+    /// </summary>
+    public string? ConditionNodeId { get; }
+
+    /// <summary>Whether this alarm can be acknowledged (active, not yet acked, has EventId).</summary>
+    public bool CanAcknowledge => ActiveState && !AckedState && EventId != null && ConditionNodeId != null;
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/AlarmsViewModel.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/AlarmsViewModel.cs
@@ -0,0 +1,225 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Opc.Ua;
+using ZB.MOM.WW.OtOpcUa.Client.Shared;
+using ZB.MOM.WW.OtOpcUa.Client.Shared.Models;
+using ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+/// <summary>
+///     ViewModel for the alarms panel.
+/// </summary>
+public partial class AlarmsViewModel : ObservableObject
+{
+    private readonly IUiDispatcher _dispatcher;
+    private readonly IOpcUaClientService _service;
+
+    [ObservableProperty] private int _interval = 1000;
+
+    [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(SubscribeCommand))]
+    [NotifyCanExecuteChangedFor(nameof(UnsubscribeCommand))]
+    [NotifyCanExecuteChangedFor(nameof(RefreshCommand))]
+    private bool _isConnected;
+
+    [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(SubscribeCommand))]
+    [NotifyCanExecuteChangedFor(nameof(UnsubscribeCommand))]
+    [NotifyCanExecuteChangedFor(nameof(RefreshCommand))]
+    private bool _isSubscribed;
+
+    [ObservableProperty] private string? _monitoredNodeIdText;
+
+    [ObservableProperty] private int _activeAlarmCount;
+
+    public AlarmsViewModel(IOpcUaClientService service, IUiDispatcher dispatcher)
+    {
+        _service = service;
+        _dispatcher = dispatcher;
+        _service.AlarmEvent += OnAlarmEvent;
+    }
+
+    /// <summary>Received alarm events.</summary>
+    public ObservableCollection<AlarmEventViewModel> AlarmEvents { get; } = [];
+
+    private void OnAlarmEvent(object? sender, AlarmEventArgs e)
+    {
+        // Only display alarm/condition events (those with a ConditionName), not generic events
+        if (string.IsNullOrEmpty(e.ConditionName)) return;
+
+        _dispatcher.Post(() =>
+        {
+            // Find existing row by source + condition and update it, or add new
+            var existing = AlarmEvents.FirstOrDefault(a =>
+                a.SourceName == e.SourceName && a.ConditionName == e.ConditionName);
+
+            if (existing != null)
+            {
+                var index = AlarmEvents.IndexOf(existing);
+                AlarmEvents[index] = new AlarmEventViewModel(
+                    e.SourceName, e.ConditionName, e.Severity, e.Message,
+                    e.Retain, e.ActiveState, e.AckedState, e.Time,
+                    e.EventId, e.ConditionNodeId);
+
+                // Remove alarms that are no longer retained
+                if (!e.Retain)
+                    AlarmEvents.RemoveAt(index);
+            }
+            else if (e.Retain)
+            {
+                AlarmEvents.Add(new AlarmEventViewModel(
+                    e.SourceName, e.ConditionName, e.Severity, e.Message,
+                    e.Retain, e.ActiveState, e.AckedState, e.Time,
+                    e.EventId, e.ConditionNodeId));
+            }
+
+            ActiveAlarmCount = AlarmEvents.Count(a => a.ActiveState && !a.AckedState);
+        });
+    }
+
+    private bool CanSubscribe()
+    {
+        return IsConnected && !IsSubscribed;
+    }
+
+    [RelayCommand(CanExecute = nameof(CanSubscribe))]
+    private async Task SubscribeAsync()
+    {
+        try
+        {
+            var sourceNodeId = string.IsNullOrWhiteSpace(MonitoredNodeIdText)
+                ? null
+                : NodeId.Parse(MonitoredNodeIdText);
+
+            await _service.SubscribeAlarmsAsync(sourceNodeId, Interval);
+            IsSubscribed = true;
+
+            try
+            {
+                await _service.RequestConditionRefreshAsync();
+            }
+            catch
+            {
+                // Refresh not supported
+            }
+        }
+        catch
+        {
+            // Subscribe failed
+        }
+    }
+
+    private bool CanUnsubscribe()
+    {
+        return IsConnected && IsSubscribed;
+    }
+
+    [RelayCommand(CanExecute = nameof(CanUnsubscribe))]
+    private async Task UnsubscribeAsync()
+    {
+        try
+        {
+            await _service.UnsubscribeAlarmsAsync();
+            IsSubscribed = false;
+        }
+        catch
+        {
+            // Unsubscribe failed
+        }
+    }
+
+    [RelayCommand(CanExecute = nameof(CanUnsubscribe))]
+    private async Task RefreshAsync()
+    {
+        try
+        {
+            await _service.RequestConditionRefreshAsync();
+        }
+        catch
+        {
+            // Refresh failed
+        }
+    }
+
+    /// <summary>
+    ///     Acknowledges an alarm and returns (success, message).
+    /// </summary>
+    public async Task<(bool Success, string Message)> AcknowledgeAlarmAsync(AlarmEventViewModel alarm, string comment)
+    {
+        if (!IsConnected || alarm.EventId == null || alarm.ConditionNodeId == null)
+            return (false, "Alarm cannot be acknowledged (missing EventId or ConditionId).");
+
+        try
+        {
+            var result = await _service.AcknowledgeAlarmAsync(alarm.ConditionNodeId, alarm.EventId, comment);
+            if (Opc.Ua.StatusCode.IsGood(result))
+                return (true, "Alarm acknowledged successfully.");
+            return (false, $"Acknowledge failed: {Helpers.StatusCodeFormatter.Format(result)}");
+        }
+        catch (Exception ex)
+        {
+            return (false, $"Error: {ex.Message}");
+        }
+    }
+
+    /// <summary>
+    ///     Returns the monitored node ID for persistence, or null if not subscribed.
+    /// </summary>
+    public string? GetAlarmSourceNodeId()
+    {
+        return IsSubscribed ? MonitoredNodeIdText : null;
+    }
+
+    /// <summary>
+    ///     Restores an alarm subscription and requests a condition refresh.
+    /// </summary>
+    public async Task RestoreAlarmSubscriptionAsync(string? sourceNodeId)
+    {
+        if (!IsConnected || string.IsNullOrWhiteSpace(sourceNodeId)) return;
+
+        MonitoredNodeIdText = sourceNodeId;
+
+        try
+        {
+            var nodeId = string.IsNullOrWhiteSpace(sourceNodeId)
+                ? null
+                : NodeId.Parse(sourceNodeId);
+
+            await _service.SubscribeAlarmsAsync(nodeId, Interval);
+            IsSubscribed = true;
+
+            try
+            {
+                await _service.RequestConditionRefreshAsync();
+            }
+            catch
+            {
+                // Refresh not supported
+            }
+        }
+        catch
+        {
+            // Subscribe failed
+        }
+    }
+
+    /// <summary>
+    ///     Clears alarm events and resets state.
+    /// </summary>
+    public void Clear()
+    {
+        AlarmEvents.Clear();
+        IsSubscribed = false;
+        ActiveAlarmCount = 0;
+    }
+
+    /// <summary>
+    ///     Unhooks event handlers from the service.
+    /// </summary>
+    public void Teardown()
+    {
+        _service.AlarmEvent -= OnAlarmEvent;
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/BrowseTreeViewModel.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/BrowseTreeViewModel.cs
@@ -0,0 +1,53 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using ZB.MOM.WW.OtOpcUa.Client.Shared;
+using ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+/// <summary>
+///     ViewModel for the OPC UA browse tree panel.
+/// </summary>
+public class BrowseTreeViewModel : ObservableObject
+{
+    private readonly IUiDispatcher _dispatcher;
+    private readonly IOpcUaClientService _service;
+
+    public BrowseTreeViewModel(IOpcUaClientService service, IUiDispatcher dispatcher)
+    {
+        _service = service;
+        _dispatcher = dispatcher;
+    }
+
+    /// <summary>Top-level nodes in the browse tree.</summary>
+    public ObservableCollection<TreeNodeViewModel> RootNodes { get; } = [];
+
+    /// <summary>
+    ///     Loads root nodes by browsing with a null parent.
+    /// </summary>
+    public async Task LoadRootsAsync()
+    {
+        var results = await _service.BrowseAsync();
+
+        _dispatcher.Post(() =>
+        {
+            RootNodes.Clear();
+            foreach (var result in results)
+                RootNodes.Add(new TreeNodeViewModel(
+                    result.NodeId,
+                    result.DisplayName,
+                    result.NodeClass,
+                    result.HasChildren,
+                    _service,
+                    _dispatcher));
+        });
+    }
+
+    /// <summary>
+    ///     Clears all root nodes from the tree.
+    /// </summary>
+    public void Clear()
+    {
+        RootNodes.Clear();
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/HistoryValueViewModel.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/HistoryValueViewModel.cs
@@ -0,0 +1,22 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+/// <summary>
+///     Represents a single historical value row.
+/// </summary>
+public class HistoryValueViewModel : ObservableObject
+{
+    public HistoryValueViewModel(string value, string status, string sourceTimestamp, string serverTimestamp)
+    {
+        Value = value;
+        Status = status;
+        SourceTimestamp = sourceTimestamp;
+        ServerTimestamp = serverTimestamp;
+    }
+
+    public string Value { get; }
+    public string Status { get; }
+    public string SourceTimestamp { get; }
+    public string ServerTimestamp { get; }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/HistoryViewModel.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/HistoryViewModel.cs
@@ -0,0 +1,133 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Opc.Ua;
+using ZB.MOM.WW.OtOpcUa.Client.Shared;
+using ZB.MOM.WW.OtOpcUa.Client.Shared.Models;
+using ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+/// <summary>
+///     ViewModel for the history panel.
+/// </summary>
+public partial class HistoryViewModel : ObservableObject
+{
+    private readonly IUiDispatcher _dispatcher;
+    private readonly IOpcUaClientService _service;
+
+    [ObservableProperty] private DateTimeOffset? _endTime = DateTimeOffset.UtcNow;
+
+    [ObservableProperty] private double _intervalMs = 3600000;
+
+    [ObservableProperty] [NotifyCanExecuteChangedFor(nameof(ReadHistoryCommand))]
+    private bool _isConnected;
+
+    [ObservableProperty] private bool _isLoading;
+
+    [ObservableProperty] private int _maxValues = 1000;
+
+    [ObservableProperty] private AggregateType? _selectedAggregateType;
+
+    [ObservableProperty] [NotifyCanExecuteChangedFor(nameof(ReadHistoryCommand))]
+    private string? _selectedNodeId;
+
+    [ObservableProperty] private DateTimeOffset? _startTime = DateTimeOffset.UtcNow.AddHours(-1);
+
+    public HistoryViewModel(IOpcUaClientService service, IUiDispatcher dispatcher)
+    {
+        _service = service;
+        _dispatcher = dispatcher;
+    }
+
+    /// <summary>Available aggregate types (null means "Raw").</summary>
+    public IReadOnlyList<AggregateType?> AggregateTypes { get; } =
+    [
+        null,
+        AggregateType.Average,
+        AggregateType.Minimum,
+        AggregateType.Maximum,
+        AggregateType.Count,
+        AggregateType.Start,
+        AggregateType.End,
+        AggregateType.StandardDeviation
+    ];
+
+    public bool IsAggregateRead => SelectedAggregateType != null;
+
+    /// <summary>History read results.</summary>
+    public ObservableCollection<HistoryValueViewModel> Results { get; } = [];
+
+    partial void OnSelectedAggregateTypeChanged(AggregateType? value)
+    {
+        OnPropertyChanged(nameof(IsAggregateRead));
+    }
+
+    private bool CanReadHistory()
+    {
+        return IsConnected && !string.IsNullOrEmpty(SelectedNodeId);
+    }
+
+    [RelayCommand(CanExecute = nameof(CanReadHistory))]
+    private async Task ReadHistoryAsync()
+    {
+        if (string.IsNullOrEmpty(SelectedNodeId)) return;
+
+        IsLoading = true;
+        _dispatcher.Post(() => Results.Clear());
+
+        try
+        {
+            var nodeId = NodeId.Parse(SelectedNodeId);
+            IReadOnlyList<DataValue> values;
+
+            var start = (StartTime ?? DateTimeOffset.UtcNow.AddHours(-1)).UtcDateTime;
+            var end = (EndTime ?? DateTimeOffset.UtcNow).UtcDateTime;
+
+            if (SelectedAggregateType != null)
+                values = await _service.HistoryReadAggregateAsync(
+                    nodeId,
+                    start,
+                    end,
+                    SelectedAggregateType.Value,
+                    IntervalMs);
+            else
+                values = await _service.HistoryReadRawAsync(
+                    nodeId,
+                    start,
+                    end,
+                    MaxValues);
+
+            _dispatcher.Post(() =>
+            {
+                foreach (var dv in values)
+                    Results.Add(new HistoryValueViewModel(
+                        Helpers.ValueFormatter.Format(dv.Value),
+                        Helpers.StatusCodeFormatter.Format(dv.StatusCode),
+                        dv.SourceTimestamp.ToString("O"),
+                        dv.ServerTimestamp.ToString("O")));
+            });
+        }
+        catch (Exception ex)
+        {
+            _dispatcher.Post(() =>
+            {
+                Results.Add(new HistoryValueViewModel(
+                    $"Error: {ex.Message}", string.Empty, string.Empty, string.Empty));
+            });
+        }
+        finally
+        {
+            _dispatcher.Post(() => IsLoading = false);
+        }
+    }
+
+    /// <summary>
+    ///     Clears results and resets state.
+    /// </summary>
+    public void Clear()
+    {
+        Results.Clear();
+        SelectedNodeId = null;
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/MainWindowViewModel.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/MainWindowViewModel.cs
@@ -0,0 +1,421 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using ZB.MOM.WW.OtOpcUa.Client.Shared;
+using ZB.MOM.WW.OtOpcUa.Client.Shared.Models;
+using ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+/// <summary>
+///     Main window ViewModel coordinating all panels.
+/// </summary>
+public partial class MainWindowViewModel : ObservableObject
+{
+    private readonly IUiDispatcher _dispatcher;
+    private readonly IOpcUaClientServiceFactory _factory;
+    private readonly ISettingsService _settingsService;
+    private IOpcUaClientService? _service;
+    private List<string> _savedSubscribedNodes = [];
+    private string? _savedAlarmSourceNodeId;
+
+    [ObservableProperty] private bool _autoAcceptCertificates = true;
+
+    [ObservableProperty] private string _certificateStorePath = Path.Combine(
+        Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+        "LmxOpcUaClient", "pki");
+
+    [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(ConnectCommand))]
+    [NotifyCanExecuteChangedFor(nameof(DisconnectCommand))]
+    private ConnectionState _connectionState = ConnectionState.Disconnected;
+
+    [ObservableProperty] private string _endpointUrl = "opc.tcp://localhost:4840";
+
+    [ObservableProperty] private string? _failoverUrls;
+
+    [ObservableProperty] private bool _isHistoryEnabledForSelection;
+
+    [ObservableProperty] private string? _password;
+
+    [ObservableProperty] private RedundancyInfo? _redundancyInfo;
+
+    [ObservableProperty] private SecurityMode _selectedSecurityMode = SecurityMode.None;
+
+    [ObservableProperty] private int _selectedTabIndex;
+
+    [ObservableProperty] private TreeNodeViewModel? _selectedTreeNode;
+
+    [ObservableProperty] private string _sessionLabel = string.Empty;
+
+    [ObservableProperty] private int _sessionTimeoutSeconds = 60;
+
+    [ObservableProperty] private string _statusMessage = "Disconnected";
+
+    [ObservableProperty] private int _subscriptionCount;
+
+    [ObservableProperty] private int _activeAlarmCount;
+
+    [ObservableProperty] private string? _username;
+
+    /// <summary>
+    /// Creates the main shell view model that coordinates connection state, browsing, subscriptions, alarms, history, and persisted settings.
+    /// </summary>
+    /// <param name="factory">Creates the shared OPC UA client service used by all panels.</param>
+    /// <param name="dispatcher">Marshals service callbacks back onto the UI thread.</param>
+    /// <param name="settingsService">Loads and saves persisted user connection settings.</param>
+    public MainWindowViewModel(IOpcUaClientServiceFactory factory, IUiDispatcher dispatcher,
+        ISettingsService? settingsService = null)
+    {
+        _factory = factory;
+        _dispatcher = dispatcher;
+        _settingsService = settingsService ?? new JsonSettingsService();
+
+        LoadSettings();
+    }
+
+    /// <summary>All available security modes.</summary>
+    public IReadOnlyList<SecurityMode> SecurityModes { get; } = Enum.GetValues<SecurityMode>();
+
+    /// <summary>
+    /// Gets a value indicating whether the shell is currently connected to an OPC UA endpoint.
+    /// </summary>
+    public bool IsConnected => ConnectionState == ConnectionState.Connected;
+
+    /// <summary>The currently selected tree nodes (supports multi-select).</summary>
+    public ObservableCollection<TreeNodeViewModel> SelectedTreeNodes { get; } = [];
+
+    /// <summary>
+    /// Gets the browse-tree panel view model for the address-space explorer.
+    /// </summary>
+    public BrowseTreeViewModel? BrowseTree { get; private set; }
+
+    /// <summary>
+    /// Gets the read/write panel view model for point operations against the selected node.
+    /// </summary>
+    public ReadWriteViewModel? ReadWrite { get; private set; }
+
+    /// <summary>
+    /// Gets the subscriptions panel view model for live data monitoring.
+    /// </summary>
+    public SubscriptionsViewModel? Subscriptions { get; private set; }
+
+    /// <summary>
+    /// Gets the alarms panel view model for active-condition monitoring and acknowledgment.
+    /// </summary>
+    public AlarmsViewModel? Alarms { get; private set; }
+
+    /// <summary>
+    /// Gets the history panel view model for raw and aggregate history queries.
+    /// </summary>
+    public HistoryViewModel? History { get; private set; }
+
+    /// <summary>
+    /// Gets the subscriptions tab header, including the current active subscription count when nonzero.
+    /// </summary>
+    public string SubscriptionsTabHeader => SubscriptionCount > 0
+        ? $"Subscriptions ({SubscriptionCount})"
+        : "Subscriptions";
+
+    /// <summary>
+    /// Gets the alarms tab header, including the current active alarm count when nonzero.
+    /// </summary>
+    public string AlarmsTabHeader => ActiveAlarmCount > 0
+        ? $"Alarms ({ActiveAlarmCount})"
+        : "Alarms";
+
+    private void InitializeService()
+    {
+        if (_service != null) return;
+
+        _service = _factory.Create();
+        _service.ConnectionStateChanged += OnConnectionStateChanged;
+
+        BrowseTree = new BrowseTreeViewModel(_service, _dispatcher);
+        ReadWrite = new ReadWriteViewModel(_service, _dispatcher);
+        Subscriptions = new SubscriptionsViewModel(_service, _dispatcher);
+        Alarms = new AlarmsViewModel(_service, _dispatcher);
+        Alarms.PropertyChanged += (_, args) =>
+        {
+            if (args.PropertyName == nameof(AlarmsViewModel.ActiveAlarmCount))
+                _dispatcher.Post(() => ActiveAlarmCount = Alarms.ActiveAlarmCount);
+        };
+        History = new HistoryViewModel(_service, _dispatcher);
+
+        OnPropertyChanged(nameof(BrowseTree));
+        OnPropertyChanged(nameof(ReadWrite));
+        OnPropertyChanged(nameof(Subscriptions));
+        OnPropertyChanged(nameof(Alarms));
+        OnPropertyChanged(nameof(History));
+    }
+
+    private void OnConnectionStateChanged(object? sender, ConnectionStateChangedEventArgs e)
+    {
+        _dispatcher.Post(() => { ConnectionState = e.NewState; });
+    }
+
+    partial void OnConnectionStateChanged(ConnectionState value)
+    {
+        OnPropertyChanged(nameof(IsConnected));
+
+        var connected = value == ConnectionState.Connected;
+        if (ReadWrite != null) ReadWrite.IsConnected = connected;
+        if (Subscriptions != null) Subscriptions.IsConnected = connected;
+        if (Alarms != null) Alarms.IsConnected = connected;
+        if (History != null) History.IsConnected = connected;
+
+        switch (value)
+        {
+            case ConnectionState.Connected:
+                StatusMessage = $"Connected to {EndpointUrl}";
+                break;
+            case ConnectionState.Reconnecting:
+                StatusMessage = "Reconnecting...";
+                break;
+            case ConnectionState.Connecting:
+                StatusMessage = "Connecting...";
+                break;
+            case ConnectionState.Disconnected:
+                StatusMessage = "Disconnected";
+                SessionLabel = string.Empty;
+                RedundancyInfo = null;
+                BrowseTree?.Clear();
+                ReadWrite?.Clear();
+                Subscriptions?.Clear();
+                Alarms?.Clear();
+                History?.Clear();
+                SubscriptionCount = 0;
+                ActiveAlarmCount = 0;
+                break;
+        }
+    }
+
+    partial void OnSelectedTreeNodeChanged(TreeNodeViewModel? value)
+    {
+        if (ReadWrite != null) ReadWrite.SelectedNodeId = value?.NodeId;
+        if (History != null) History.SelectedNodeId = value?.NodeId;
+    }
+
+    partial void OnSubscriptionCountChanged(int value)
+    {
+        OnPropertyChanged(nameof(SubscriptionsTabHeader));
+    }
+
+    partial void OnActiveAlarmCountChanged(int value)
+    {
+        OnPropertyChanged(nameof(AlarmsTabHeader));
+    }
+
+    private bool CanConnect()
+    {
+        return ConnectionState == ConnectionState.Disconnected;
+    }
+
+    [RelayCommand(CanExecute = nameof(CanConnect))]
+    private async Task ConnectAsync()
+    {
+        try
+        {
+            ConnectionState = ConnectionState.Connecting;
+            StatusMessage = "Connecting...";
+
+            InitializeService();
+
+            var settings = new ConnectionSettings
+            {
+                EndpointUrl = EndpointUrl,
+                Username = Username,
+                Password = Password,
+                SecurityMode = SelectedSecurityMode,
+                FailoverUrls = ParseFailoverUrls(FailoverUrls),
+                SessionTimeoutSeconds = SessionTimeoutSeconds,
+                AutoAcceptCertificates = AutoAcceptCertificates,
+                CertificateStorePath = CertificateStorePath
+            };
+            settings.Validate();
+
+            var info = await _service!.ConnectAsync(settings);
+
+            _dispatcher.Post(() =>
+            {
+                ConnectionState = ConnectionState.Connected;
+                SessionLabel = $"{info.ServerName} | Session: {info.SessionName} ({info.SessionId})";
+            });
+
+            // Load redundancy info
+            try
+            {
+                var redundancy = await _service!.GetRedundancyInfoAsync();
+                _dispatcher.Post(() => RedundancyInfo = redundancy);
+            }
+            catch
+            {
+                // Redundancy info not available
+            }
+
+            // Load root nodes
+            await BrowseTree.LoadRootsAsync();
+
+            // Restore saved subscriptions
+            if (_savedSubscribedNodes.Count > 0 && Subscriptions != null)
+            {
+                await Subscriptions.RestoreSubscriptionsAsync(_savedSubscribedNodes);
+                SubscriptionCount = Subscriptions.SubscriptionCount;
+            }
+
+            // Restore saved alarm subscription
+            if (!string.IsNullOrEmpty(_savedAlarmSourceNodeId) && Alarms != null)
+                await Alarms.RestoreAlarmSubscriptionAsync(_savedAlarmSourceNodeId);
+
+            SaveSettings();
+        }
+        catch (Exception ex)
+        {
+            _dispatcher.Post(() =>
+            {
+                ConnectionState = ConnectionState.Disconnected;
+                StatusMessage = $"Connection failed: {ex.Message}";
+            });
+        }
+    }
+
+    private bool CanDisconnect()
+    {
+        return ConnectionState == ConnectionState.Connected
+               || ConnectionState == ConnectionState.Reconnecting;
+    }
+
+    [RelayCommand(CanExecute = nameof(CanDisconnect))]
+    private async Task DisconnectAsync()
+    {
+        try
+        {
+            SaveSettings();
+            Subscriptions?.Teardown();
+            Alarms?.Teardown();
+            await _service!.DisconnectAsync();
+        }
+        catch
+        {
+            // Best-effort disconnect
+        }
+        finally
+        {
+            _dispatcher.Post(() => { ConnectionState = ConnectionState.Disconnected; });
+        }
+    }
+
+    /// <summary>
+    ///     Subscribes all selected tree nodes and switches to the Subscriptions tab.
+    /// </summary>
+    [RelayCommand]
+    private async Task SubscribeSelectedNodesAsync()
+    {
+        if (SelectedTreeNodes.Count == 0 || !IsConnected) return;
+
+        if (Subscriptions == null) return;
+
+        var nodes = SelectedTreeNodes.ToList();
+        foreach (var node in nodes)
+            await Subscriptions.AddSubscriptionRecursiveAsync(node.NodeId, node.NodeClass);
+
+        SubscriptionCount = Subscriptions.SubscriptionCount;
+        SelectedTabIndex = 1; // Subscriptions tab
+    }
+
+    /// <summary>
+    ///     Sets the history tab's selected node and switches to the History tab.
+    /// </summary>
+    [RelayCommand]
+    private void ViewHistoryForSelectedNode()
+    {
+        if (SelectedTreeNodes.Count == 0 || !IsConnected) return;
+
+        var node = SelectedTreeNodes[0];
+        History.SelectedNodeId = node.NodeId;
+        SelectedTabIndex = 3; // History tab
+    }
+
+    /// <summary>
+    ///     Stops any active alarm subscription, subscribes to alarms on the selected node,
+    ///     and switches to the Alarms tab.
+    /// </summary>
+    [RelayCommand]
+    private async Task MonitorAlarmsForSelectedNodeAsync()
+    {
+        if (SelectedTreeNodes.Count == 0 || !IsConnected || Alarms == null) return;
+
+        var node = SelectedTreeNodes[0];
+
+        // Stop existing alarm subscription if active
+        if (Alarms.IsSubscribed)
+        {
+            try { await _service!.UnsubscribeAlarmsAsync(); }
+            catch { /* best effort */ }
+            Alarms.Clear();
+        }
+
+        // Subscribe to the selected node
+        Alarms.MonitoredNodeIdText = node.NodeId;
+        await Alarms.SubscribeCommand.ExecuteAsync(null);
+
+        SelectedTabIndex = 2; // Alarms tab
+    }
+
+    /// <summary>
+    ///     Updates whether "View History" should be enabled based on the selected node's type.
+    ///     Only Variable nodes can have history.
+    /// </summary>
+    public void UpdateHistoryEnabledForSelection()
+    {
+        IsHistoryEnabledForSelection = IsConnected
+                                       && SelectedTreeNodes.Count > 0
+                                       && SelectedTreeNodes[0].NodeClass == "Variable";
+    }
+
+    private void LoadSettings()
+    {
+        var s = _settingsService.Load();
+        EndpointUrl = s.EndpointUrl;
+        Username = s.Username;
+        Password = s.Password;
+        SelectedSecurityMode = s.SecurityMode;
+        FailoverUrls = s.FailoverUrls;
+        SessionTimeoutSeconds = s.SessionTimeoutSeconds;
+        AutoAcceptCertificates = s.AutoAcceptCertificates;
+        if (!string.IsNullOrEmpty(s.CertificateStorePath))
+            CertificateStorePath = s.CertificateStorePath;
+        _savedSubscribedNodes = s.SubscribedNodes;
+        _savedAlarmSourceNodeId = s.AlarmSourceNodeId;
+    }
+
+    /// <summary>
+    /// Persists the current connection, subscription, and alarm-monitoring settings for the next UI session.
+    /// </summary>
+    public void SaveSettings()
+    {
+        _settingsService.Save(new UserSettings
+        {
+            EndpointUrl = EndpointUrl,
+            Username = Username,
+            Password = Password,
+            SecurityMode = SelectedSecurityMode,
+            FailoverUrls = FailoverUrls,
+            SessionTimeoutSeconds = SessionTimeoutSeconds,
+            AutoAcceptCertificates = AutoAcceptCertificates,
+            CertificateStorePath = CertificateStorePath,
+            SubscribedNodes = Subscriptions?.GetSubscribedNodeIds() ?? _savedSubscribedNodes,
+            AlarmSourceNodeId = Alarms?.GetAlarmSourceNodeId() ?? _savedAlarmSourceNodeId
+        });
+    }
+
+    private static string[]? ParseFailoverUrls(string? csv)
+    {
+        if (string.IsNullOrWhiteSpace(csv))
+            return null;
+
+        return csv.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
+            .Where(u => !string.IsNullOrEmpty(u))
+            .ToArray();
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/ReadWriteViewModel.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/ReadWriteViewModel.cs
@@ -0,0 +1,124 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Opc.Ua;
+using ZB.MOM.WW.OtOpcUa.Client.Shared;
+using ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+/// <summary>
+///     ViewModel for the read/write panel.
+/// </summary>
+public partial class ReadWriteViewModel : ObservableObject
+{
+    private readonly IUiDispatcher _dispatcher;
+    private readonly IOpcUaClientService _service;
+
+    [ObservableProperty] private string? _currentStatus;
+
+    [ObservableProperty] private string? _currentValue;
+
+    [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(ReadCommand))]
+    [NotifyCanExecuteChangedFor(nameof(WriteCommand))]
+    private bool _isConnected;
+
+    [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(ReadCommand))]
+    [NotifyCanExecuteChangedFor(nameof(WriteCommand))]
+    private string? _selectedNodeId;
+
+    [ObservableProperty] private string? _serverTimestamp;
+
+    [ObservableProperty] private string? _sourceTimestamp;
+
+    [ObservableProperty] private string? _writeStatus;
+
+    [ObservableProperty] private string? _writeValue;
+
+    public ReadWriteViewModel(IOpcUaClientService service, IUiDispatcher dispatcher)
+    {
+        _service = service;
+        _dispatcher = dispatcher;
+    }
+
+    public bool IsNodeSelected => !string.IsNullOrEmpty(SelectedNodeId);
+
+    partial void OnSelectedNodeIdChanged(string? value)
+    {
+        OnPropertyChanged(nameof(IsNodeSelected));
+        if (!string.IsNullOrEmpty(value) && IsConnected) _ = ExecuteReadAsync();
+    }
+
+    private bool CanReadOrWrite()
+    {
+        return IsConnected && !string.IsNullOrEmpty(SelectedNodeId);
+    }
+
+    [RelayCommand(CanExecute = nameof(CanReadOrWrite))]
+    private async Task ReadAsync()
+    {
+        await ExecuteReadAsync();
+    }
+
+    private async Task ExecuteReadAsync()
+    {
+        if (string.IsNullOrEmpty(SelectedNodeId)) return;
+
+        try
+        {
+            var nodeId = NodeId.Parse(SelectedNodeId);
+            var dataValue = await _service.ReadValueAsync(nodeId);
+
+            _dispatcher.Post(() =>
+            {
+                CurrentValue = Helpers.ValueFormatter.Format(dataValue.Value);
+                CurrentStatus = Helpers.StatusCodeFormatter.Format(dataValue.StatusCode);
+                SourceTimestamp = dataValue.SourceTimestamp.ToString("O");
+                ServerTimestamp = dataValue.ServerTimestamp.ToString("O");
+            });
+        }
+        catch (Exception ex)
+        {
+            _dispatcher.Post(() =>
+            {
+                CurrentValue = null;
+                CurrentStatus = $"Error: {ex.Message}";
+                SourceTimestamp = null;
+                ServerTimestamp = null;
+            });
+        }
+    }
+
+    [RelayCommand(CanExecute = nameof(CanReadOrWrite))]
+    private async Task WriteAsync()
+    {
+        if (string.IsNullOrEmpty(SelectedNodeId) || WriteValue == null) return;
+
+        try
+        {
+            var nodeId = NodeId.Parse(SelectedNodeId);
+            var statusCode = await _service.WriteValueAsync(nodeId, WriteValue);
+
+            _dispatcher.Post(() => { WriteStatus = statusCode.ToString(); });
+        }
+        catch (Exception ex)
+        {
+            _dispatcher.Post(() => { WriteStatus = $"Error: {ex.Message}"; });
+        }
+    }
+
+    /// <summary>
+    ///     Clears all displayed values.
+    /// </summary>
+    public void Clear()
+    {
+        SelectedNodeId = null;
+        CurrentValue = null;
+        CurrentStatus = null;
+        SourceTimestamp = null;
+        ServerTimestamp = null;
+        WriteValue = null;
+        WriteStatus = null;
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/SubscriptionItemViewModel.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/SubscriptionItemViewModel.cs
@@ -0,0 +1,27 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+/// <summary>
+///     Represents a single active subscription row.
+/// </summary>
+public partial class SubscriptionItemViewModel : ObservableObject
+{
+    [ObservableProperty] private string? _status;
+
+    [ObservableProperty] private string? _timestamp;
+
+    [ObservableProperty] private string? _value;
+
+    public SubscriptionItemViewModel(string nodeId, int intervalMs)
+    {
+        NodeId = nodeId;
+        IntervalMs = intervalMs;
+    }
+
+    /// <summary>The monitored NodeId.</summary>
+    public string NodeId { get; }
+
+    /// <summary>The subscription interval in milliseconds.</summary>
+    public int IntervalMs { get; }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/SubscriptionsViewModel.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/SubscriptionsViewModel.cs
@@ -0,0 +1,275 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Opc.Ua;
+using ZB.MOM.WW.OtOpcUa.Client.Shared;
+using ZB.MOM.WW.OtOpcUa.Client.Shared.Models;
+using ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+/// <summary>
+///     ViewModel for the subscriptions panel.
+/// </summary>
+public partial class SubscriptionsViewModel : ObservableObject
+{
+    private readonly IUiDispatcher _dispatcher;
+    private readonly IOpcUaClientService _service;
+
+    [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(AddSubscriptionCommand))]
+    [NotifyCanExecuteChangedFor(nameof(RemoveSubscriptionCommand))]
+    private bool _isConnected;
+
+    [ObservableProperty] private int _newInterval = 1000;
+
+    [ObservableProperty] [NotifyCanExecuteChangedFor(nameof(AddSubscriptionCommand))]
+    private string? _newNodeIdText;
+
+    [ObservableProperty] [NotifyCanExecuteChangedFor(nameof(RemoveSubscriptionCommand))]
+    private SubscriptionItemViewModel? _selectedSubscription;
+
+    [ObservableProperty] private int _subscriptionCount;
+
+    /// <summary>
+    /// Creates the subscriptions panel view model used to manage live data subscriptions and ad hoc writes from the UI.
+    /// </summary>
+    /// <param name="service">The shared client service that performs subscribe, unsubscribe, read, and write operations.</param>
+    /// <param name="dispatcher">Marshals data-change callbacks back onto the UI thread.</param>
+    public SubscriptionsViewModel(IOpcUaClientService service, IUiDispatcher dispatcher)
+    {
+        _service = service;
+        _dispatcher = dispatcher;
+        _service.DataChanged += OnDataChanged;
+    }
+
+    /// <summary>Currently active subscriptions.</summary>
+    public ObservableCollection<SubscriptionItemViewModel> ActiveSubscriptions { get; } = [];
+
+    /// <summary>Currently selected subscriptions (for multi-select remove).</summary>
+    public List<SubscriptionItemViewModel> SelectedSubscriptions { get; } = [];
+
+    private void OnDataChanged(object? sender, DataChangedEventArgs e)
+    {
+        _dispatcher.Post(() =>
+        {
+            foreach (var item in ActiveSubscriptions)
+                if (item.NodeId == e.NodeId)
+                {
+                    item.Value = Helpers.ValueFormatter.Format(e.Value.Value);
+                    item.Status = Helpers.StatusCodeFormatter.Format(e.Value.StatusCode);
+                    item.Timestamp = e.Value.SourceTimestamp.ToString("O");
+                }
+        });
+    }
+
+    private bool CanAddSubscription()
+    {
+        return IsConnected && !string.IsNullOrWhiteSpace(NewNodeIdText);
+    }
+
+    [RelayCommand(CanExecute = nameof(CanAddSubscription))]
+    private async Task AddSubscriptionAsync()
+    {
+        if (string.IsNullOrWhiteSpace(NewNodeIdText)) return;
+
+        var nodeIdStr = NewNodeIdText;
+        var interval = NewInterval;
+
+        try
+        {
+            var nodeId = NodeId.Parse(nodeIdStr);
+            await _service.SubscribeAsync(nodeId, interval);
+
+            _dispatcher.Post(() =>
+            {
+                ActiveSubscriptions.Add(new SubscriptionItemViewModel(nodeIdStr, interval));
+                SubscriptionCount = ActiveSubscriptions.Count;
+            });
+        }
+        catch
+        {
+            // Subscription failed; no item added
+        }
+    }
+
+    private bool CanRemoveSubscription()
+    {
+        return IsConnected && (SelectedSubscriptions.Count > 0 || SelectedSubscription != null);
+    }
+
+    [RelayCommand(CanExecute = nameof(CanRemoveSubscription))]
+    private async Task RemoveSubscriptionAsync()
+    {
+        var itemsToRemove = SelectedSubscriptions.Count > 0
+            ? SelectedSubscriptions.ToList()
+            : SelectedSubscription != null ? [SelectedSubscription] : [];
+
+        if (itemsToRemove.Count == 0) return;
+
+        foreach (var item in itemsToRemove)
+        {
+            try
+            {
+                var nodeId = NodeId.Parse(item.NodeId);
+                await _service.UnsubscribeAsync(nodeId);
+
+                _dispatcher.Post(() => ActiveSubscriptions.Remove(item));
+            }
+            catch
+            {
+                // Unsubscribe failed for this item; continue with others
+            }
+        }
+
+        _dispatcher.Post(() => SubscriptionCount = ActiveSubscriptions.Count);
+    }
+
+    /// <summary>
+    ///     Subscribes to a node by ID (used by context menu). Skips if already subscribed.
+    /// </summary>
+    /// <param name="nodeIdStr">The node ID to subscribe to from the browse tree or persisted settings.</param>
+    /// <param name="intervalMs">The monitored-item interval, in milliseconds, for the subscription.</param>
+    public async Task AddSubscriptionForNodeAsync(string nodeIdStr, int intervalMs = 1000)
+    {
+        if (!IsConnected || string.IsNullOrWhiteSpace(nodeIdStr)) return;
+
+        // Skip if already subscribed
+        if (ActiveSubscriptions.Any(s => s.NodeId == nodeIdStr)) return;
+
+        try
+        {
+            var nodeId = NodeId.Parse(nodeIdStr);
+            await _service.SubscribeAsync(nodeId, intervalMs);
+
+            _dispatcher.Post(() =>
+            {
+                ActiveSubscriptions.Add(new SubscriptionItemViewModel(nodeIdStr, intervalMs));
+                SubscriptionCount = ActiveSubscriptions.Count;
+            });
+        }
+        catch
+        {
+            // Subscription failed
+        }
+    }
+
+    /// <summary>
+    ///     Subscribes to a node and all its Variable descendants recursively.
+    ///     Object nodes are browsed for children; Variable nodes are subscribed directly.
+    /// </summary>
+    /// <param name="nodeIdStr">The root node whose variables should be subscribed recursively.</param>
+    /// <param name="nodeClass">The node class of the starting node so variables can be subscribed immediately.</param>
+    /// <param name="intervalMs">The monitored-item interval, in milliseconds, used for created subscriptions.</param>
+    public Task AddSubscriptionRecursiveAsync(string nodeIdStr, string nodeClass, int intervalMs = 1000)
+    {
+        return AddSubscriptionRecursiveAsync(nodeIdStr, nodeClass, intervalMs, maxDepth: 10, currentDepth: 0);
+    }
+
+    private async Task AddSubscriptionRecursiveAsync(string nodeIdStr, string nodeClass, int intervalMs, int maxDepth, int currentDepth)
+    {
+        if (!IsConnected || string.IsNullOrWhiteSpace(nodeIdStr)) return;
+        if (currentDepth >= maxDepth) return;
+
+        if (nodeClass == "Variable")
+        {
+            await AddSubscriptionForNodeAsync(nodeIdStr, intervalMs);
+            return;
+        }
+
+        // Browse children and recurse
+        try
+        {
+            var nodeId = NodeId.Parse(nodeIdStr);
+            var children = await _service.BrowseAsync(nodeId);
+
+            foreach (var child in children)
+                await AddSubscriptionRecursiveAsync(child.NodeId, child.NodeClass, intervalMs, maxDepth, currentDepth + 1);
+        }
+        catch
+        {
+            // Browse failed for this node; skip it
+        }
+    }
+
+    /// <summary>
+    ///     Returns the node IDs of all active subscriptions for persistence.
+    /// </summary>
+    public List<string> GetSubscribedNodeIds()
+    {
+        return ActiveSubscriptions.Select(s => s.NodeId).ToList();
+    }
+
+    /// <summary>
+    ///     Restores subscriptions from a saved list of node IDs.
+    /// </summary>
+    /// <param name="nodeIds">The node IDs persisted from a prior UI session.</param>
+    public async Task RestoreSubscriptionsAsync(IEnumerable<string> nodeIds)
+    {
+        foreach (var nodeId in nodeIds)
+            await AddSubscriptionForNodeAsync(nodeId);
+    }
+
+    /// <summary>
+    ///     Reads the current value of a node to determine its type, validates that the raw
+    ///     input can be parsed to that type, writes the value, and returns (success, message).
+    /// </summary>
+    /// <param name="nodeIdStr">The node ID the operator wants to write.</param>
+    /// <param name="rawValue">The raw text value entered by the operator.</param>
+    public async Task<(bool Success, string Message)> ValidateAndWriteAsync(string nodeIdStr, string rawValue)
+    {
+        try
+        {
+            var nodeId = NodeId.Parse(nodeIdStr);
+
+            // Read current value to determine target type
+            var currentDataValue = await _service.ReadValueAsync(nodeId);
+            var currentValue = currentDataValue.Value;
+
+            // Try parsing to the target type before writing
+            try
+            {
+                Shared.Helpers.ValueConverter.ConvertValue(rawValue, currentValue);
+            }
+            catch (FormatException ex)
+            {
+                var typeName = currentValue?.GetType().Name ?? "unknown";
+                return (false, $"Cannot parse \"{rawValue}\" as {typeName}: {ex.Message}");
+            }
+            catch (OverflowException ex)
+            {
+                var typeName = currentValue?.GetType().Name ?? "unknown";
+                return (false, $"Value \"{rawValue}\" is out of range for {typeName}: {ex.Message}");
+            }
+
+            var result = await _service.WriteValueAsync(nodeId, rawValue);
+            var statusText = Helpers.StatusCodeFormatter.Format(result);
+
+            if (Opc.Ua.StatusCode.IsGood(result))
+                return (true, statusText);
+
+            return (false, $"Write failed: {statusText}");
+        }
+        catch (Exception ex)
+        {
+            return (false, $"Error: {ex.Message}");
+        }
+    }
+
+    /// <summary>
+    ///     Clears all subscriptions and resets state.
+    /// </summary>
+    public void Clear()
+    {
+        ActiveSubscriptions.Clear();
+        SubscriptionCount = 0;
+    }
+
+    /// <summary>
+    ///     Unhooks event handlers from the service.
+    /// </summary>
+    public void Teardown()
+    {
+        _service.DataChanged -= OnDataChanged;
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/TreeNodeViewModel.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/TreeNodeViewModel.cs
@@ -0,0 +1,111 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using ZB.MOM.WW.OtOpcUa.Client.Shared;
+using ZB.MOM.WW.OtOpcUa.Client.UI.Services;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+/// <summary>
+///     Represents a single node in the OPC UA browse tree with lazy-load support.
+/// </summary>
+public partial class TreeNodeViewModel : ObservableObject
+{
+    private static readonly TreeNodeViewModel PlaceholderSentinel = new();
+    private readonly IUiDispatcher? _dispatcher;
+
+    private readonly IOpcUaClientService? _service;
+    private bool _hasLoadedChildren;
+
+    [ObservableProperty] private bool _isExpanded;
+
+    [ObservableProperty] private bool _isLoading;
+
+    /// <summary>
+    ///     Private constructor for the placeholder sentinel only.
+    /// </summary>
+    private TreeNodeViewModel()
+    {
+        NodeId = string.Empty;
+        DisplayName = "Loading...";
+        NodeClass = string.Empty;
+        HasChildren = false;
+    }
+
+    public TreeNodeViewModel(
+        string nodeId,
+        string displayName,
+        string nodeClass,
+        bool hasChildren,
+        IOpcUaClientService service,
+        IUiDispatcher dispatcher)
+    {
+        NodeId = nodeId;
+        DisplayName = displayName;
+        NodeClass = nodeClass;
+        HasChildren = hasChildren;
+        _service = service;
+        _dispatcher = dispatcher;
+
+        if (hasChildren) Children.Add(PlaceholderSentinel);
+    }
+
+    /// <summary>The string NodeId of this node.</summary>
+    public string NodeId { get; }
+
+    /// <summary>The display name shown in the tree.</summary>
+    public string DisplayName { get; }
+
+    /// <summary>The OPC UA node class (Object, Variable, etc.).</summary>
+    public string NodeClass { get; }
+
+    /// <summary>Whether this node has child references.</summary>
+    public bool HasChildren { get; }
+
+    /// <summary>Child nodes (may contain a placeholder sentinel before first expand).</summary>
+    public ObservableCollection<TreeNodeViewModel> Children { get; } = [];
+
+    /// <summary>
+    ///     Returns whether this node instance is the placeholder sentinel.
+    /// </summary>
+    internal bool IsPlaceholder => ReferenceEquals(this, PlaceholderSentinel);
+
+    partial void OnIsExpandedChanged(bool value)
+    {
+        if (value && !_hasLoadedChildren && HasChildren) _ = LoadChildrenAsync();
+    }
+
+    private async Task LoadChildrenAsync()
+    {
+        if (_service == null || _dispatcher == null) return;
+
+        _hasLoadedChildren = true;
+        IsLoading = true;
+
+        try
+        {
+            var nodeId = Opc.Ua.NodeId.Parse(NodeId);
+            var results = await _service.BrowseAsync(nodeId);
+
+            _dispatcher.Post(() =>
+            {
+                Children.Clear();
+                foreach (var result in results)
+                    Children.Add(new TreeNodeViewModel(
+                        result.NodeId,
+                        result.DisplayName,
+                        result.NodeClass,
+                        result.HasChildren,
+                        _service,
+                        _dispatcher));
+            });
+        }
+        catch
+        {
+            _dispatcher.Post(() => Children.Clear());
+        }
+        finally
+        {
+            _dispatcher.Post(() => IsLoading = false);
+        }
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/AckAlarmWindow.axaml
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/AckAlarmWindow.axaml
@@ -0,0 +1,39 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.AckAlarmWindow"
+        Title="Acknowledge Alarm"
+        Width="420"
+        SizeToContent="Height"
+        MinHeight="240"
+        WindowStartupLocation="CenterOwner"
+        CanResize="False">
+    <StackPanel Margin="16" Spacing="12">
+        <TextBlock Text="Acknowledge Alarm" FontWeight="Bold" FontSize="16" />
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="Source:" FontSize="12" Foreground="Gray" />
+            <TextBlock Name="SourceText" FontWeight="SemiBold" />
+        </StackPanel>
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="Condition:" FontSize="12" Foreground="Gray" />
+            <TextBlock Name="ConditionText" />
+        </StackPanel>
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="Comment:" FontSize="12" Foreground="Gray" />
+            <TextBox Name="CommentInput"
+                     Watermark="Enter acknowledgment comment"
+                     AcceptsReturn="True"
+                     Height="60"
+                     TextWrapping="Wrap" />
+        </StackPanel>
+
+        <TextBlock Name="ResultText" Foreground="Gray" />
+
+        <StackPanel Orientation="Horizontal" Spacing="8" HorizontalAlignment="Right">
+            <Button Name="AckButton" Content="Acknowledge" />
+            <Button Name="CancelButton" Content="Cancel" />
+        </StackPanel>
+    </StackPanel>
+</Window>
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/AckAlarmWindow.axaml.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/AckAlarmWindow.axaml.cs
@@ -0,0 +1,67 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Media;
+using ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class AckAlarmWindow : Window
+{
+    private readonly AlarmsViewModel _alarmsVm;
+    private readonly AlarmEventViewModel _alarm;
+
+    public AckAlarmWindow()
+    {
+        InitializeComponent();
+        _alarmsVm = null!;
+        _alarm = null!;
+    }
+
+    public AckAlarmWindow(AlarmsViewModel alarmsVm, AlarmEventViewModel alarm)
+    {
+        InitializeComponent();
+        _alarmsVm = alarmsVm;
+        _alarm = alarm;
+
+        var sourceText = this.FindControl<TextBlock>("SourceText");
+        if (sourceText != null) sourceText.Text = alarm.SourceName;
+
+        var conditionText = this.FindControl<TextBlock>("ConditionText");
+        if (conditionText != null) conditionText.Text = $"{alarm.ConditionName} (Severity: {alarm.Severity})";
+
+        var ackButton = this.FindControl<Button>("AckButton");
+        if (ackButton != null) ackButton.Click += OnAckClicked;
+
+        var cancelButton = this.FindControl<Button>("CancelButton");
+        if (cancelButton != null) cancelButton.Click += OnCancelClicked;
+    }
+
+    private async void OnAckClicked(object? sender, RoutedEventArgs e)
+    {
+        var commentInput = this.FindControl<TextBox>("CommentInput");
+        var resultText = this.FindControl<TextBlock>("ResultText");
+        if (commentInput == null || resultText == null) return;
+
+        var comment = commentInput.Text ?? string.Empty;
+
+        resultText.Foreground = Brushes.Gray;
+        resultText.Text = "Acknowledging...";
+
+        var (success, message) = await _alarmsVm.AcknowledgeAlarmAsync(_alarm, comment);
+
+        if (success)
+        {
+            Close();
+        }
+        else
+        {
+            resultText.Foreground = Brushes.Red;
+            resultText.Text = message;
+        }
+    }
+
+    private void OnCancelClicked(object? sender, RoutedEventArgs e)
+    {
+        Close();
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/AlarmsView.axaml
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/AlarmsView.axaml
@@ -0,0 +1,39 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels"
+             x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.AlarmsView"
+             x:DataType="vm:AlarmsViewModel">
+    <DockPanel Margin="8">
+        <!-- Controls -->
+        <StackPanel DockPanel.Dock="Top" Spacing="8">
+            <TextBlock Text="Alarm Monitoring" FontWeight="Bold" />
+            <StackPanel Orientation="Horizontal" Spacing="8">
+                <TextBox Text="{Binding MonitoredNodeIdText}" Width="250" Watermark="Source Node ID (optional)" />
+                <NumericUpDown Value="{Binding Interval}" Minimum="100" Maximum="60000" Width="120" />
+                <Button Content="Subscribe" Command="{Binding SubscribeCommand}" />
+                <Button Content="Unsubscribe" Command="{Binding UnsubscribeCommand}" />
+                <Button Content="Refresh" Command="{Binding RefreshCommand}" />
+            </StackPanel>
+        </StackPanel>
+
+        <!-- Alarm Events -->
+        <DataGrid Name="AlarmsGrid"
+                  ItemsSource="{Binding AlarmEvents}"
+                  AutoGenerateColumns="False"
+                  IsReadOnly="True"
+                  HorizontalScrollBarVisibility="Auto"
+                  Margin="0,8,0,0"
+                  LoadingRow="OnDataGridLoadingRow">
+            <DataGrid.Columns>
+                <DataGridTextColumn Header="Time" Binding="{Binding Time, StringFormat='{}{0:yyyy-MM-dd HH:mm:ss}'}" Width="Auto" />
+                <DataGridTextColumn Header="Source" Binding="{Binding SourceName}" Width="Auto" />
+                <DataGridTextColumn Header="Condition" Binding="{Binding ConditionName}" Width="Auto" />
+                <DataGridTextColumn Header="Severity" Binding="{Binding Severity}" Width="Auto" />
+                <DataGridTextColumn Header="Message" Binding="{Binding Message}" Width="Auto" />
+                <DataGridCheckBoxColumn Header="Active" Binding="{Binding ActiveState}" Width="Auto" />
+                <DataGridCheckBoxColumn Header="Acked" Binding="{Binding AckedState}" Width="Auto" />
+                <DataGridCheckBoxColumn Header="Retain" Binding="{Binding Retain}" Width="Auto" />
+            </DataGrid.Columns>
+        </DataGrid>
+    </DockPanel>
+</UserControl>
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/AlarmsView.axaml.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/AlarmsView.axaml.cs
@@ -0,0 +1,79 @@
+using System.ComponentModel;
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Media;
+using Avalonia.VisualTree;
+using ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class AlarmsView : UserControl
+{
+    // Severity color bands (OPC UA severity 0-1000)
+    private static readonly IBrush InactiveBrush = new SolidColorBrush(Color.Parse("#F0F0F0"));     // light grey
+    private static readonly IBrush LowBrush = new SolidColorBrush(Color.Parse("#DBEAFE"));          // light blue (1-332)
+    private static readonly IBrush MediumBrush = new SolidColorBrush(Color.Parse("#FEF3C7"));       // light yellow (333-665)
+    private static readonly IBrush HighBrush = new SolidColorBrush(Color.Parse("#FEE2E2"));         // light red (666-899)
+    private static readonly IBrush CriticalBrush = new SolidColorBrush(Color.Parse("#FECACA"));     // red (900-1000)
+
+    public AlarmsView()
+    {
+        InitializeComponent();
+    }
+
+    protected override void OnLoaded(RoutedEventArgs e)
+    {
+        base.OnLoaded(e);
+
+        var grid = this.FindControl<DataGrid>("AlarmsGrid");
+        if (grid == null) return;
+
+        var contextMenu = new ContextMenu();
+        var ackItem = new MenuItem { Header = "Acknowledge..." };
+        ackItem.Click += OnAcknowledgeClicked;
+        contextMenu.Items.Add(ackItem);
+        contextMenu.Opening += OnContextMenuOpening;
+        grid.ContextMenu = contextMenu;
+    }
+
+    private void OnDataGridLoadingRow(object? sender, DataGridRowEventArgs e)
+    {
+        if (e.Row.DataContext is AlarmEventViewModel alarm)
+            e.Row.Background = GetSeverityBrush(alarm);
+    }
+
+    private static IBrush GetSeverityBrush(AlarmEventViewModel alarm)
+    {
+        if (!alarm.ActiveState)
+            return InactiveBrush;
+
+        return alarm.Severity switch
+        {
+            >= 900 => CriticalBrush,
+            >= 666 => HighBrush,
+            >= 333 => MediumBrush,
+            _ => LowBrush
+        };
+    }
+
+    private void OnContextMenuOpening(object? sender, CancelEventArgs e)
+    {
+        var grid = this.FindControl<DataGrid>("AlarmsGrid");
+        if (grid?.SelectedItem is not AlarmEventViewModel alarm || !alarm.CanAcknowledge)
+            e.Cancel = true;
+    }
+
+    private void OnAcknowledgeClicked(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is not AlarmsViewModel vm) return;
+
+        var grid = this.FindControl<DataGrid>("AlarmsGrid");
+        if (grid?.SelectedItem is not AlarmEventViewModel alarm || !alarm.CanAcknowledge) return;
+
+        var parentWindow = this.FindAncestorOfType<Window>();
+        if (parentWindow == null) return;
+
+        var ackWindow = new AckAlarmWindow(vm, alarm);
+        ackWindow.ShowDialog(parentWindow);
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/BrowseTreeView.axaml
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/BrowseTreeView.axaml
@@ -0,0 +1,31 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels"
+             x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.BrowseTreeView"
+             x:DataType="vm:BrowseTreeViewModel">
+    <TreeView ItemsSource="{Binding RootNodes}"
+              Name="BrowseTree"
+              SelectionMode="Multiple">
+        <TreeView.Styles>
+            <Style Selector="TreeViewItem" x:DataType="vm:TreeNodeViewModel">
+                <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
+            </Style>
+        </TreeView.Styles>
+        <TreeView.ItemTemplate>
+            <TreeDataTemplate ItemsSource="{Binding Children}">
+                <StackPanel Orientation="Horizontal" Spacing="6">
+                    <TextBlock Text="{Binding DisplayName}" VerticalAlignment="Center" />
+                    <TextBlock Text="{Binding NodeClass}"
+                               FontSize="10"
+                               Foreground="Gray"
+                               VerticalAlignment="Center" />
+                    <ProgressBar IsIndeterminate="True"
+                                 IsVisible="{Binding IsLoading}"
+                                 Width="50"
+                                 Height="8"
+                                 VerticalAlignment="Center" />
+                </StackPanel>
+            </TreeDataTemplate>
+        </TreeView.ItemTemplate>
+    </TreeView>
+</UserControl>
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/BrowseTreeView.axaml.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/BrowseTreeView.axaml.cs
@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class BrowseTreeView : UserControl
+{
+    public BrowseTreeView()
+    {
+        InitializeComponent();
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/HistoryView.axaml
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/HistoryView.axaml
@@ -0,0 +1,65 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels"
+             xmlns:controls="using:ZB.MOM.WW.OtOpcUa.Client.UI.Controls"
+             x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.HistoryView"
+             x:DataType="vm:HistoryViewModel">
+    <DockPanel Margin="8">
+        <!-- Controls -->
+        <StackPanel DockPanel.Dock="Top" Spacing="10">
+            <TextBlock Text="History Read" FontWeight="Bold" />
+            <TextBlock Text="{Binding SelectedNodeId, FallbackValue='(no node selected)'}"
+                       Foreground="Gray" />
+
+            <!-- Row 1: Time range -->
+            <controls:DateTimeRangePicker StartDateTime="{Binding StartTime, Mode=TwoWay}"
+                                          EndDateTime="{Binding EndTime, Mode=TwoWay}" />
+
+            <!-- Row 2: Aggregate, Interval, Max Values, Read button -->
+            <StackPanel Orientation="Horizontal" Spacing="12">
+                <StackPanel Spacing="2">
+                    <TextBlock Text="Aggregate" FontSize="11" Foreground="Gray" />
+                    <ComboBox ItemsSource="{Binding AggregateTypes}"
+                              SelectedItem="{Binding SelectedAggregateType}"
+                              Width="150">
+                        <ComboBox.ItemTemplate>
+                            <DataTemplate>
+                                <TextBlock Text="{Binding, TargetNullValue='Raw'}" />
+                            </DataTemplate>
+                        </ComboBox.ItemTemplate>
+                    </ComboBox>
+                </StackPanel>
+                <StackPanel Spacing="2" IsVisible="{Binding IsAggregateRead}">
+                    <TextBlock Text="Interval (ms)" FontSize="11" Foreground="Gray" />
+                    <NumericUpDown Value="{Binding IntervalMs}" Minimum="1000" Maximum="86400000" Width="150" />
+                </StackPanel>
+                <StackPanel Spacing="2">
+                    <TextBlock Text="Max Values" FontSize="11" Foreground="Gray" />
+                    <NumericUpDown Value="{Binding MaxValues}" Minimum="1" Maximum="100000" Width="120" />
+                </StackPanel>
+                <Button Content="Read History"
+                        Command="{Binding ReadHistoryCommand}"
+                        VerticalAlignment="Bottom"
+                        Padding="16,6" />
+            </StackPanel>
+
+            <ProgressBar IsIndeterminate="True"
+                         IsVisible="{Binding IsLoading}"
+                         Height="4" />
+        </StackPanel>
+
+        <!-- Results -->
+        <DataGrid ItemsSource="{Binding Results}"
+                  AutoGenerateColumns="False"
+                  IsReadOnly="True"
+                  HorizontalScrollBarVisibility="Auto"
+                  Margin="0,8,0,0">
+            <DataGrid.Columns>
+                <DataGridTextColumn Header="Value" Binding="{Binding Value}" Width="Auto" />
+                <DataGridTextColumn Header="Status" Binding="{Binding Status}" Width="Auto" />
+                <DataGridTextColumn Header="Source Timestamp" Binding="{Binding SourceTimestamp}" Width="Auto" />
+                <DataGridTextColumn Header="Server Timestamp" Binding="{Binding ServerTimestamp}" Width="Auto" />
+            </DataGrid.Columns>
+        </DataGrid>
+    </DockPanel>
+</UserControl>
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/HistoryView.axaml.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/HistoryView.axaml.cs
@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class HistoryView : UserControl
+{
+    public HistoryView()
+    {
+        InitializeComponent();
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/MainWindow.axaml
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/MainWindow.axaml
@@ -0,0 +1,162 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="using:ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels"
+        xmlns:views="using:ZB.MOM.WW.OtOpcUa.Client.UI.Views"
+        x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.MainWindow"
+        x:DataType="vm:MainWindowViewModel"
+        Title="OPC UA Client"
+        Width="1200"
+        Height="800">
+    <DockPanel>
+        <!-- Top Connection Bar -->
+        <Border DockPanel.Dock="Top" Background="#F0F0F0" Padding="12">
+            <StackPanel Spacing="4">
+                <!-- Always visible: URL + Connect/Disconnect -->
+                <StackPanel Orientation="Horizontal" Spacing="8">
+                    <StackPanel Spacing="2" VerticalAlignment="Bottom">
+                        <TextBlock Text="Endpoint URL" FontSize="11" Foreground="Gray" />
+                        <TextBox Text="{Binding EndpointUrl}"
+                                 Width="400"
+                                 Watermark="opc.tcp://host:port" />
+                    </StackPanel>
+                    <Button Content="Connect"
+                            Command="{Binding ConnectCommand}"
+                            VerticalAlignment="Bottom" Padding="16,6" />
+                    <Button Content="Disconnect"
+                            Command="{Binding DisconnectCommand}"
+                            VerticalAlignment="Bottom" Padding="16,6" />
+                </StackPanel>
+
+                <!-- Expandable settings -->
+                <Expander Header="Connection Settings" Padding="0,4">
+                    <StackPanel Spacing="10" Margin="4,8,4,4">
+                        <!-- Row 1: Authentication -->
+                        <StackPanel Orientation="Horizontal" Spacing="12">
+                            <StackPanel Spacing="2">
+                                <TextBlock Text="Username" FontSize="11" Foreground="Gray" />
+                                <TextBox Text="{Binding Username}"
+                                         Width="160"
+                                         Watermark="(anonymous)" />
+                            </StackPanel>
+                            <StackPanel Spacing="2">
+                                <TextBlock Text="Password" FontSize="11" Foreground="Gray" />
+                                <TextBox Text="{Binding Password}"
+                                         Width="160"
+                                         Watermark="(none)"
+                                         PasswordChar="*" />
+                            </StackPanel>
+                            <StackPanel Spacing="2">
+                                <TextBlock Text="Security Mode" FontSize="11" Foreground="Gray" />
+                                <ComboBox ItemsSource="{Binding SecurityModes}"
+                                          SelectedItem="{Binding SelectedSecurityMode}"
+                                          Width="160" />
+                            </StackPanel>
+                        </StackPanel>
+
+                        <!-- Row 2: Failover + Session -->
+                        <StackPanel Orientation="Horizontal" Spacing="12">
+                            <StackPanel Spacing="2">
+                                <TextBlock Text="Failover URLs (comma-separated)" FontSize="11" Foreground="Gray" />
+                                <TextBox Text="{Binding FailoverUrls}"
+                                         Width="400"
+                                         Watermark="opc.tcp://backup1:4840, opc.tcp://backup2:4840" />
+                            </StackPanel>
+                            <StackPanel Spacing="2">
+                                <TextBlock Text="Session Timeout (s)" FontSize="11" Foreground="Gray" />
+                                <NumericUpDown Value="{Binding SessionTimeoutSeconds}"
+                                               Minimum="1" Maximum="3600"
+                                               Width="120"
+                                               FormatString="0" />
+                            </StackPanel>
+                        </StackPanel>
+
+                        <!-- Row 3: Certificates -->
+                        <StackPanel Orientation="Horizontal" Spacing="12">
+                            <StackPanel Spacing="2">
+                                <TextBlock Text="Certificate Store Path" FontSize="11" Foreground="Gray" />
+                                <StackPanel Orientation="Horizontal" Spacing="4">
+                                    <TextBox Text="{Binding CertificateStorePath}"
+                                             Width="370"
+                                             IsReadOnly="True"
+                                             Watermark="(default: AppData/LmxOpcUaClient/pki)" />
+                                    <Button Name="BrowseCertPathButton"
+                                            Content="..."
+                                            Width="30"
+                                            ToolTip.Tip="Browse for folder" />
+                                </StackPanel>
+                            </StackPanel>
+                            <CheckBox IsChecked="{Binding AutoAcceptCertificates}"
+                                      Content="Auto-accept untrusted server certificates"
+                                      VerticalAlignment="Bottom"
+                                      Margin="0,0,0,4" />
+                        </StackPanel>
+                    </StackPanel>
+                </Expander>
+
+                <!-- Redundancy Info -->
+                <StackPanel Orientation="Horizontal"
+                            Spacing="16"
+                            IsVisible="{Binding RedundancyInfo, Converter={x:Static ObjectConverters.IsNotNull}}"
+                            Margin="0,2,0,0">
+                    <TextBlock Text="{Binding RedundancyInfo.Mode, StringFormat='Redundancy: {0}'}"
+                               FontSize="11" Foreground="Gray" />
+                    <TextBlock Text="{Binding RedundancyInfo.ServiceLevel, StringFormat='Service Level: {0}'}"
+                               FontSize="11" Foreground="Gray" />
+                    <TextBlock Text="{Binding RedundancyInfo.ApplicationUri, StringFormat='URI: {0}'}"
+                               FontSize="11" Foreground="Gray" />
+                </StackPanel>
+            </StackPanel>
+        </Border>
+
+        <!-- Bottom Status Bar -->
+        <Border DockPanel.Dock="Bottom" Background="#F0F0F0" Padding="8,4">
+            <StackPanel Orientation="Horizontal" Spacing="20">
+                <TextBlock Text="{Binding StatusMessage}" />
+                <TextBlock Text="{Binding SessionLabel}" Foreground="Gray" />
+                <TextBlock Text="{Binding SubscriptionCount, StringFormat='Subscriptions: {0}'}" />
+            </StackPanel>
+        </Border>
+
+        <!-- Main Content -->
+        <Grid ColumnDefinitions="300,8,*">
+            <!-- Left: Browse Tree -->
+            <Border Grid.Column="0" BorderBrush="#CCCCCC" BorderThickness="0,0,1,0">
+                <DockPanel>
+                    <TextBlock DockPanel.Dock="Top" Text="Browse Tree" FontWeight="Bold" Margin="8,8,8,4" />
+                    <views:BrowseTreeView DataContext="{Binding BrowseTree}"
+                                          Name="BrowseTreePanel">
+                        <views:BrowseTreeView.ContextMenu>
+                            <ContextMenu Name="TreeContextMenu">
+                                <MenuItem Header="Subscribe" Name="SubscribeMenuItem" />
+                                <MenuItem Header="View History" Name="ViewHistoryMenuItem" />
+                                <Separator />
+                                <MenuItem Header="Monitor Alarms" Name="MonitorAlarmsMenuItem" />
+                            </ContextMenu>
+                        </views:BrowseTreeView.ContextMenu>
+                    </views:BrowseTreeView>
+                </DockPanel>
+            </Border>
+
+            <!-- Splitter -->
+            <GridSplitter Grid.Column="1" Width="8" Background="Transparent" />
+
+            <!-- Right: Tab panels -->
+            <TabControl Grid.Column="2"
+                        IsEnabled="{Binding IsConnected}"
+                        SelectedIndex="{Binding SelectedTabIndex}">
+                <TabItem Header="Read/Write">
+                    <views:ReadWriteView DataContext="{Binding ReadWrite}" />
+                </TabItem>
+                <TabItem Header="{Binding SubscriptionsTabHeader}">
+                    <views:SubscriptionsView DataContext="{Binding Subscriptions}" />
+                </TabItem>
+                <TabItem Header="{Binding AlarmsTabHeader}">
+                    <views:AlarmsView DataContext="{Binding Alarms}" />
+                </TabItem>
+                <TabItem Header="History">
+                    <views:HistoryView DataContext="{Binding History}" />
+                </TabItem>
+            </TabControl>
+        </Grid>
+    </DockPanel>
+</Window>
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/MainWindow.axaml.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/MainWindow.axaml.cs
@@ -0,0 +1,146 @@
+using System.ComponentModel;
+using System.Reflection;
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using SkiaSharp;
+using Svg.Skia;
+using ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class MainWindow : Window
+{
+    public MainWindow()
+    {
+        InitializeComponent();
+        LoadIcon();
+    }
+
+    private void LoadIcon()
+    {
+        try
+        {
+            var assembly = Assembly.GetExecutingAssembly();
+            using var stream = assembly.GetManifestResourceStream("ZB.MOM.WW.OtOpcUa.Client.UI.Assets.app-icon.svg");
+            if (stream == null) return;
+
+            using var svg = new SKSvg();
+            svg.Load(stream);
+            if (svg.Picture == null) return;
+
+            var size = 64;
+            using var bitmap = new SKBitmap(size, size);
+            using var canvas = new SKCanvas(bitmap);
+            canvas.Clear(SKColors.Transparent);
+
+            var bounds = svg.Picture.CullRect;
+            var scale = Math.Min(size / bounds.Width, size / bounds.Height);
+            canvas.Translate((size - bounds.Width * scale) / 2, (size - bounds.Height * scale) / 2);
+            canvas.Scale(scale);
+            canvas.DrawPicture(svg.Picture);
+
+            using var image = SKImage.FromBitmap(bitmap);
+            using var data = image.Encode(SKEncodedImageFormat.Png, 100);
+            using var pngStream = new MemoryStream(data.ToArray());
+            Icon = new WindowIcon(pngStream);
+        }
+        catch
+        {
+            // Icon loading is best-effort
+        }
+    }
+
+    protected override void OnLoaded(RoutedEventArgs e)
+    {
+        base.OnLoaded(e);
+
+        var browseTreeView = this.FindControl<BrowseTreeView>("BrowseTreePanel");
+        var treeView = browseTreeView?.FindControl<TreeView>("BrowseTree");
+        if (treeView != null) treeView.SelectionChanged += OnTreeSelectionChanged;
+
+        var contextMenu = this.FindControl<ContextMenu>("TreeContextMenu");
+        if (contextMenu != null) contextMenu.Opening += OnTreeContextMenuOpening;
+
+        var subscribeItem = this.FindControl<MenuItem>("SubscribeMenuItem");
+        if (subscribeItem != null) subscribeItem.Click += OnSubscribeClicked;
+
+        var viewHistoryItem = this.FindControl<MenuItem>("ViewHistoryMenuItem");
+        if (viewHistoryItem != null) viewHistoryItem.Click += OnViewHistoryClicked;
+
+        var monitorAlarmsItem = this.FindControl<MenuItem>("MonitorAlarmsMenuItem");
+        if (monitorAlarmsItem != null) monitorAlarmsItem.Click += OnMonitorAlarmsClicked;
+
+        var browseCertPath = this.FindControl<Button>("BrowseCertPathButton");
+        if (browseCertPath != null) browseCertPath.Click += OnBrowseCertPathClicked;
+    }
+
+    private void OnTreeSelectionChanged(object? sender, SelectionChangedEventArgs e)
+    {
+        if (DataContext is not MainWindowViewModel vm || sender is not TreeView treeView) return;
+
+        vm.SelectedTreeNode = treeView.SelectedItem as TreeNodeViewModel;
+
+        vm.SelectedTreeNodes.Clear();
+        foreach (var item in treeView.SelectedItems)
+            if (item is TreeNodeViewModel node)
+                vm.SelectedTreeNodes.Add(node);
+    }
+
+    private void OnTreeContextMenuOpening(object? sender, CancelEventArgs e)
+    {
+        if (DataContext is not MainWindowViewModel vm) return;
+
+        vm.UpdateHistoryEnabledForSelection();
+
+        var subscribeItem = this.FindControl<MenuItem>("SubscribeMenuItem");
+        var viewHistoryItem = this.FindControl<MenuItem>("ViewHistoryMenuItem");
+        var monitorAlarmsItem = this.FindControl<MenuItem>("MonitorAlarmsMenuItem");
+
+        if (subscribeItem != null)
+            subscribeItem.IsEnabled = vm.IsConnected && vm.SelectedTreeNodes.Count > 0;
+        if (viewHistoryItem != null)
+            viewHistoryItem.IsEnabled = vm.IsHistoryEnabledForSelection;
+        if (monitorAlarmsItem != null)
+            monitorAlarmsItem.IsEnabled = vm.IsConnected && vm.SelectedTreeNodes.Count > 0;
+    }
+
+    private async void OnSubscribeClicked(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is MainWindowViewModel vm)
+            await vm.SubscribeSelectedNodesCommand.ExecuteAsync(null);
+    }
+
+    private void OnViewHistoryClicked(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is MainWindowViewModel vm)
+            vm.ViewHistoryForSelectedNodeCommand.Execute(null);
+    }
+
+    private async void OnMonitorAlarmsClicked(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is MainWindowViewModel vm)
+            await vm.MonitorAlarmsForSelectedNodeCommand.ExecuteAsync(null);
+    }
+
+    private async void OnBrowseCertPathClicked(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is not MainWindowViewModel vm) return;
+
+        var dialog = new OpenFolderDialog
+        {
+            Title = "Select Certificate Store Folder",
+            Directory = vm.CertificateStorePath
+        };
+
+        var result = await dialog.ShowAsync(this);
+        if (!string.IsNullOrEmpty(result))
+            vm.CertificateStorePath = result;
+    }
+
+    protected override void OnClosing(WindowClosingEventArgs e)
+    {
+        if (DataContext is MainWindowViewModel vm)
+            vm.SaveSettings();
+        base.OnClosing(e);
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/ReadWriteView.axaml
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/ReadWriteView.axaml
@@ -0,0 +1,39 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels"
+             x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.ReadWriteView"
+             x:DataType="vm:ReadWriteViewModel">
+    <StackPanel Spacing="8" Margin="8">
+        <!-- Selected Node -->
+        <TextBlock Text="Selected Node" FontWeight="Bold" />
+        <TextBlock Text="{Binding SelectedNodeId, FallbackValue='(none)'}"
+                   Foreground="Gray" />
+
+        <!-- Read Section -->
+        <Separator />
+        <TextBlock Text="Read Value" FontWeight="Bold" />
+        <Button Content="Read" Command="{Binding ReadCommand}" />
+        <Grid ColumnDefinitions="Auto,*" RowDefinitions="Auto,Auto,Auto,Auto" Margin="0,4,0,0">
+            <TextBlock Grid.Row="0" Grid.Column="0" Text="Value: " FontWeight="SemiBold" />
+            <TextBlock Grid.Row="0" Grid.Column="1" Text="{Binding CurrentValue}" TextWrapping="Wrap" />
+
+            <TextBlock Grid.Row="1" Grid.Column="0" Text="Status: " FontWeight="SemiBold" />
+            <TextBlock Grid.Row="1" Grid.Column="1" Text="{Binding CurrentStatus}" />
+
+            <TextBlock Grid.Row="2" Grid.Column="0" Text="Source Time: " FontWeight="SemiBold" />
+            <TextBlock Grid.Row="2" Grid.Column="1" Text="{Binding SourceTimestamp}" />
+
+            <TextBlock Grid.Row="3" Grid.Column="0" Text="Server Time: " FontWeight="SemiBold" />
+            <TextBlock Grid.Row="3" Grid.Column="1" Text="{Binding ServerTimestamp}" />
+        </Grid>
+
+        <!-- Write Section -->
+        <Separator />
+        <TextBlock Text="Write Value" FontWeight="Bold" />
+        <StackPanel Orientation="Horizontal" Spacing="8">
+            <TextBox Text="{Binding WriteValue}" Width="200" Watermark="Value to write" />
+            <Button Content="Write" Command="{Binding WriteCommand}" />
+        </StackPanel>
+        <TextBlock Text="{Binding WriteStatus}" Foreground="Gray" />
+    </StackPanel>
+</UserControl>
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/ReadWriteView.axaml.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/ReadWriteView.axaml.cs
@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class ReadWriteView : UserControl
+{
+    public ReadWriteView()
+    {
+        InitializeComponent();
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/SubscriptionsView.axaml
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/SubscriptionsView.axaml
@@ -0,0 +1,35 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels"
+             x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.SubscriptionsView"
+             x:DataType="vm:SubscriptionsViewModel">
+    <DockPanel Margin="8">
+        <!-- Add/Remove Controls -->
+        <StackPanel DockPanel.Dock="Top" Spacing="8">
+            <TextBlock Text="Subscriptions" FontWeight="Bold" />
+            <StackPanel Orientation="Horizontal" Spacing="8">
+                <TextBox Text="{Binding NewNodeIdText}" Width="250" Watermark="Node ID (e.g., ns=2;s=MyNode)" />
+                <NumericUpDown Value="{Binding NewInterval}" Minimum="100" Maximum="60000" Width="120" />
+                <Button Content="Add" Command="{Binding AddSubscriptionCommand}" />
+                <Button Content="Remove" Command="{Binding RemoveSubscriptionCommand}" />
+            </StackPanel>
+        </StackPanel>
+
+        <!-- Active Subscriptions List -->
+        <DataGrid Name="SubscriptionsGrid"
+                  ItemsSource="{Binding ActiveSubscriptions}"
+                  SelectedItem="{Binding SelectedSubscription}"
+                  SelectionMode="Extended"
+                  AutoGenerateColumns="False"
+                  IsReadOnly="True"
+                  HorizontalScrollBarVisibility="Auto"
+                  Margin="0,8,0,0">
+            <DataGrid.Columns>
+                <DataGridTextColumn Header="Node ID" Binding="{Binding NodeId}" Width="Auto" />
+                <DataGridTextColumn Header="Value" Binding="{Binding Value}" Width="Auto" />
+                <DataGridTextColumn Header="Status" Binding="{Binding Status}" Width="Auto" />
+                <DataGridTextColumn Header="Timestamp" Binding="{Binding Timestamp}" Width="Auto" />
+            </DataGrid.Columns>
+        </DataGrid>
+    </DockPanel>
+</UserControl>
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/SubscriptionsView.axaml.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/SubscriptionsView.axaml.cs
@@ -0,0 +1,51 @@
+using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Interactivity;
+using Avalonia.VisualTree;
+using ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class SubscriptionsView : UserControl
+{
+    public SubscriptionsView()
+    {
+        InitializeComponent();
+    }
+
+    protected override void OnLoaded(RoutedEventArgs e)
+    {
+        base.OnLoaded(e);
+
+        var grid = this.FindControl<DataGrid>("SubscriptionsGrid");
+        if (grid != null)
+        {
+            grid.DoubleTapped += OnGridDoubleTapped;
+            grid.SelectionChanged += OnGridSelectionChanged;
+        }
+    }
+
+    private void OnGridSelectionChanged(object? sender, SelectionChangedEventArgs e)
+    {
+        if (DataContext is not SubscriptionsViewModel vm || sender is not DataGrid grid) return;
+
+        vm.SelectedSubscriptions.Clear();
+        foreach (var item in grid.SelectedItems)
+            if (item is SubscriptionItemViewModel sub)
+                vm.SelectedSubscriptions.Add(sub);
+
+        vm.RemoveSubscriptionCommand.NotifyCanExecuteChanged();
+    }
+
+    private void OnGridDoubleTapped(object? sender, TappedEventArgs e)
+    {
+        if (DataContext is not SubscriptionsViewModel vm) return;
+        if (vm.SelectedSubscription is not { } item) return;
+
+        var parentWindow = this.FindAncestorOfType<Window>();
+        if (parentWindow == null) return;
+
+        var writeWindow = new WriteValueWindow(vm, item.NodeId, item.Value);
+        writeWindow.ShowDialog(parentWindow);
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/WriteValueWindow.axaml
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/WriteValueWindow.axaml
@@ -0,0 +1,37 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.WriteValueWindow"
+        Title="Write Value"
+        Width="420"
+        SizeToContent="Height"
+        MinHeight="280"
+        WindowStartupLocation="CenterOwner"
+        CanResize="False">
+    <StackPanel Margin="16" Spacing="12">
+        <TextBlock Text="Write Value to Node" FontWeight="Bold" FontSize="16" />
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="Node ID:" FontSize="12" Foreground="Gray" />
+            <TextBlock Name="NodeIdText" FontWeight="SemiBold" />
+        </StackPanel>
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="Current Value:" FontSize="12" Foreground="Gray" />
+            <TextBlock Name="CurrentValueText" />
+        </StackPanel>
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="New Value:" FontSize="12" Foreground="Gray" />
+            <TextBox Name="WriteValueInput" Watermark="Enter value to write" />
+        </StackPanel>
+
+        <StackPanel Spacing="4">
+            <TextBlock Name="ResultText" Foreground="Gray" />
+        </StackPanel>
+
+        <StackPanel Orientation="Horizontal" Spacing="8" HorizontalAlignment="Right">
+            <Button Name="WriteButton" Content="Write" />
+            <Button Name="CloseButton" Content="Close" />
+        </StackPanel>
+    </StackPanel>
+</Window>
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/WriteValueWindow.axaml.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/WriteValueWindow.axaml.cs
@@ -0,0 +1,77 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Media;
+using ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class WriteValueWindow : Window
+{
+    private readonly SubscriptionsViewModel _subscriptionsVm;
+    private readonly string _nodeId;
+
+    public WriteValueWindow()
+    {
+        InitializeComponent();
+        _subscriptionsVm = null!;
+        _nodeId = string.Empty;
+    }
+
+    public WriteValueWindow(SubscriptionsViewModel subscriptionsVm, string nodeId, string? currentValue)
+    {
+        InitializeComponent();
+        _subscriptionsVm = subscriptionsVm;
+        _nodeId = nodeId;
+
+        var nodeIdText = this.FindControl<TextBlock>("NodeIdText");
+        if (nodeIdText != null) nodeIdText.Text = nodeId;
+
+        var currentValueText = this.FindControl<TextBlock>("CurrentValueText");
+        if (currentValueText != null) currentValueText.Text = currentValue ?? "(null)";
+
+        // Pre-fill the write input with the current value
+        var writeInput = this.FindControl<TextBox>("WriteValueInput");
+        if (writeInput != null) writeInput.Text = currentValue ?? "";
+
+        var writeButton = this.FindControl<Button>("WriteButton");
+        if (writeButton != null) writeButton.Click += OnWriteClicked;
+
+        var closeButton = this.FindControl<Button>("CloseButton");
+        if (closeButton != null) closeButton.Click += OnCloseClicked;
+    }
+
+    private async void OnWriteClicked(object? sender, RoutedEventArgs e)
+    {
+        var input = this.FindControl<TextBox>("WriteValueInput");
+        var resultText = this.FindControl<TextBlock>("ResultText");
+        if (input == null || resultText == null) return;
+
+        var rawValue = input.Text;
+        if (string.IsNullOrEmpty(rawValue))
+        {
+            resultText.Foreground = Brushes.Red;
+            resultText.Text = "Please enter a value.";
+            return;
+        }
+
+        resultText.Foreground = Brushes.Gray;
+        resultText.Text = "Writing...";
+
+        var (success, message) = await _subscriptionsVm.ValidateAndWriteAsync(_nodeId, rawValue);
+
+        if (success)
+        {
+            Close();
+        }
+        else
+        {
+            resultText.Foreground = Brushes.Red;
+            resultText.Text = message;
+        }
+    }
+
+    private void OnCloseClicked(object? sender, RoutedEventArgs e)
+    {
+        Close();
+    }
+}
--- a/src/ZB.MOM.WW.OtOpcUa.Client.UI/ZB.MOM.WW.OtOpcUa.Client.UI.csproj
+++ b/src/ZB.MOM.WW.OtOpcUa.Client.UI/ZB.MOM.WW.OtOpcUa.Client.UI.csproj
@@ -0,0 +1,37 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>WinExe</OutputType>
+        <TargetFramework>net10.0</TargetFramework>
+        <Nullable>enable</Nullable>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Client.UI</RootNamespace>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="Avalonia" Version="11.2.7"/>
+        <PackageReference Include="Avalonia.Desktop" Version="11.2.7"/>
+        <PackageReference Include="Avalonia.Svg.Skia" Version="11.2.0.2"/>
+        <PackageReference Include="Avalonia.Themes.Fluent" Version="11.2.7"/>
+        <PackageReference Include="Avalonia.Fonts.Inter" Version="11.2.7"/>
+        <PackageReference Include="Avalonia.Controls.DataGrid" Version="11.2.7"/>
+        <PackageReference Include="Avalonia.Diagnostics" Version="11.2.7"/>
+        <PackageReference Include="CommunityToolkit.Mvvm" Version="8.4.0"/>
+        <PackageReference Include="Serilog" Version="4.2.0"/>
+        <PackageReference Include="Serilog.Sinks.Console" Version="6.0.0"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Client.Shared\ZB.MOM.WW.OtOpcUa.Client.Shared.csproj"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.Client.UI.Tests"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <AvaloniaResource Include="Assets\**" Exclude="Assets\app-icon.svg" />
+        <EmbeddedResource Include="Assets\app-icon.svg" />
+    </ItemGroup>
+
+</Project>