diff --git a/src/ScadaLink.Commons/Messages/Notification/NotificationOutboxQueries.cs b/src/ScadaLink.Commons/Messages/Notification/NotificationOutboxQueries.cs
index 6fbb1b2..20f68d9 100644
--- a/src/ScadaLink.Commons/Messages/Notification/NotificationOutboxQueries.cs
+++ b/src/ScadaLink.Commons/Messages/Notification/NotificationOutboxQueries.cs
@@ -1,3 +1,5 @@
+using ScadaLink.Commons.Types.Notifications;
+
 namespace ScadaLink.Commons.Messages.Notification;
 
 /// <summary>
@@ -94,3 +96,20 @@ public record NotificationKpiResponse(
     int ParkedCount,
     int DeliveredLastInterval,
     TimeSpan? OldestPendingAge);
+
+/// <summary>
+/// Outbox UI -> Central: request for the per-source-site notification outbox KPI breakdown.
+/// </summary>
+public record PerSiteNotificationKpiRequest(
+    string CorrelationId);
+
+/// <summary>
+/// Central -> Outbox UI: per-site KPI breakdown for the Notification KPIs page.
+/// On a repository fault <see cref="Success"/> is <c>false</c>, <see cref="ErrorMessage"/>
+/// carries the cause, and <see cref="Sites"/> is empty.
+/// </summary>
+public record PerSiteNotificationKpiResponse(
+    string CorrelationId,
+    bool Success,
+    string? ErrorMessage,
+    IReadOnlyList<SiteNotificationKpiSnapshot> Sites);
diff --git a/tests/ScadaLink.Commons.Tests/Messages/NotificationMessagesTests.cs b/tests/ScadaLink.Commons.Tests/Messages/NotificationMessagesTests.cs
index 2b171c8..f68996f 100644
--- a/tests/ScadaLink.Commons.Tests/Messages/NotificationMessagesTests.cs
+++ b/tests/ScadaLink.Commons.Tests/Messages/NotificationMessagesTests.cs
@@ -1,4 +1,5 @@
 using ScadaLink.Commons.Messages.Notification;
+using ScadaLink.Commons.Types.Notifications;
 
 namespace ScadaLink.Commons.Tests.Messages;
 
@@ -187,4 +188,26 @@ public class NotificationMessagesTests
         var msg = new NotificationKpiRequest("corr-1");
         Assert.Equal("corr-1", msg.CorrelationId);
     }
+
+    [Fact]
+    public void PerSiteNotificationKpiRequest_CarriesCorrelationId()
+    {
+        var request = new PerSiteNotificationKpiRequest("corr-1");
+        Assert.Equal("corr-1", request.CorrelationId);
+    }
+
+    [Fact]
+    public void PerSiteNotificationKpiResponse_CarriesPerSiteSnapshots()
+    {
+        var sites = new[]
+        {
+            new SiteNotificationKpiSnapshot("plant-a", 3, 1, 0, 10, TimeSpan.FromMinutes(4)),
+        };
+        var response = new PerSiteNotificationKpiResponse("corr-1", Success: true, ErrorMessage: null, sites);
+
+        Assert.True(response.Success);
+        Assert.Null(response.ErrorMessage);
+        Assert.Single(response.Sites);
+        Assert.Equal("plant-a", response.Sites[0].SourceSiteId);
+    }
 }