diff --git a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Shared/TreeView.razor b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Shared/TreeView.razor
index 0d1be6fd..c0f4be8e 100644
--- a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Shared/TreeView.razor
+++ b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Shared/TreeView.razor
@@ -51,7 +51,15 @@ else
                 @oncontextmenu="(e) => OnContextMenu(e, item)" @oncontextmenu:preventDefault="@(ContextMenu != null)" @oncontextmenu:stopPropagation="@(ContextMenu != null)">
                 @if (isBranch)
                 {
-                    <span class="tv-toggle" @onclick="() => ToggleExpand(key)" @onclick:stopPropagation><i class="bi bi-chevron-right"></i></span>
+                    <span class="tv-toggle"
+                          role="button"
+                          tabindex="0"
+                          aria-label="@((isExpanded ? "Collapse " : "Expand ") + KeyStr(key))"
+                          aria-expanded="@(isExpanded ? "true" : "false")"
+                          @onclick="() => ToggleExpand(key)"
+                          @onclick:stopPropagation
+                          @onkeydown="(e) => OnToggleKey(e, key)"
+                          @onkeydown:preventDefault><i class="bi bi-chevron-right"></i></span>
                 }
                 else
                 {
@@ -276,6 +284,14 @@ else
         PersistExpandedState();
     }
 
+    private void OnToggleKey(KeyboardEventArgs e, object key)
+    {
+        if (e.Key == "Enter" || e.Key == " ")
+        {
+            ToggleExpand(key);
+        }
+    }
+
     private void PersistExpandedState()
     {
         if (StorageKey != null)
diff --git a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Shared/AccessibilityTests.cs b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Shared/AccessibilityTests.cs
new file mode 100644
index 00000000..69e814d0
--- /dev/null
+++ b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Shared/AccessibilityTests.cs
@@ -0,0 +1,106 @@
+using Bunit;
+using Microsoft.AspNetCore.Components;
+using ZB.MOM.WW.ScadaBridge.CentralUI.Components.Shared;
+
+namespace ZB.MOM.WW.ScadaBridge.CentralUI.Tests.Shared;
+
+/// <summary>
+/// Accessibility regression tests.
+/// Locks the a11y attributes on TreeView chevron toggles and the
+/// ToastNotification live-region container against future regressions.
+/// </summary>
+public class AccessibilityTests : BunitContext
+{
+    // ── TreeView harness (mirrors TreeViewTests setup) ─────────────────────────
+
+    private record TestNode(string Key, string Label, List<TestNode> Children);
+
+    private static List<TestNode> BranchRoots() => new()
+    {
+        new("root-1", "Root One", new()
+        {
+            new("child-1", "Child One", new()),
+        }),
+        new("leaf-1", "Leaf One", new()),
+    };
+
+    private IRenderedComponent<TreeView<TestNode>> RenderTreeView(List<TestNode>? items = null)
+    {
+        return Render<TreeView<TestNode>>(parameters =>
+        {
+            parameters
+                .Add(p => p.Items, items ?? BranchRoots())
+                .Add(p => p.ChildrenSelector, n => n.Children)
+                .Add(p => p.HasChildrenSelector, n => n.Children.Count > 0)
+                .Add(p => p.KeySelector, n => n.Key)
+                .Add(p => p.NodeContent, node => builder =>
+                {
+                    builder.AddMarkupContent(0, $"<span class=\"node-label\">{node.Label}</span>");
+                });
+        });
+    }
+
+    // ── Test 1: TreeView chevron toggle a11y attributes ────────────────────────
+
+    [Fact]
+    public void TreeViewToggle_HasAccessibleNameAndRole()
+    {
+        // BranchRoots has one branch node ("root-1") and one leaf node ("leaf-1").
+        // The branch node's toggle span is the only .tv-toggle rendered.
+        var cut = RenderTreeView();
+
+        var toggle = cut.Find(".tv-toggle");
+
+        // role="button" makes it announced as a button by screen readers.
+        Assert.Equal("button", toggle.GetAttribute("role"));
+
+        // tabindex="0" puts it in the natural tab order.
+        Assert.Equal("0", toggle.GetAttribute("tabindex"));
+
+        // aria-label must be non-empty (e.g. "Expand root-1").
+        var label = toggle.GetAttribute("aria-label");
+        Assert.NotNull(label);
+        Assert.NotEmpty(label!);
+
+        // aria-expanded reflects the collapsed state ("false" when collapsed).
+        Assert.Equal("false", toggle.GetAttribute("aria-expanded"));
+    }
+
+    [Fact]
+    public void TreeViewToggle_AriaExpanded_ReflectsExpandedState()
+    {
+        var cut = RenderTreeView();
+
+        // Collapsed initially.
+        var toggle = cut.Find(".tv-toggle");
+        Assert.Equal("false", toggle.GetAttribute("aria-expanded"));
+
+        // Click to expand.
+        toggle.Click();
+
+        // aria-expanded must now be "true".
+        var expandedToggle = cut.Find(".tv-toggle");
+        Assert.Equal("true", expandedToggle.GetAttribute("aria-expanded"));
+
+        // aria-label should also flip to "Collapse …".
+        var labelAfterExpand = expandedToggle.GetAttribute("aria-label");
+        Assert.NotNull(labelAfterExpand);
+        Assert.StartsWith("Collapse", labelAfterExpand!);
+    }
+
+    // ── Test 2: ToastNotification live-region regression lock ─────────────────
+
+    [Fact]
+    public void ToastNotification_Container_IsAriaLivePolite()
+    {
+        // Render ToastNotification — it has no required services/cascading params.
+        var cut = Render<ToastNotification>();
+
+        // The outermost div is the live-region container.
+        // Find the element that carries aria-live (may be the root or a child div).
+        var liveRegion = cut.Find("[aria-live]");
+
+        Assert.Equal("polite", liveRegion.GetAttribute("aria-live"));
+        Assert.Equal("true", liveRegion.GetAttribute("aria-atomic"));
+    }
+}