diff --git a/src/ScadaLink.ConfigurationDatabase/Repositories/NotificationOutboxRepository.cs b/src/ScadaLink.ConfigurationDatabase/Repositories/NotificationOutboxRepository.cs
index 28fe593..78bab14 100644
--- a/src/ScadaLink.ConfigurationDatabase/Repositories/NotificationOutboxRepository.cs
+++ b/src/ScadaLink.ConfigurationDatabase/Repositories/NotificationOutboxRepository.cs
@@ -174,6 +174,68 @@ public class NotificationOutboxRepository : INotificationOutboxRepository
             OldestPendingAge: oldestPendingAge);
     }
 
+    public async Task<IReadOnlyList<SiteNotificationKpiSnapshot>> ComputePerSiteKpisAsync(
+        DateTimeOffset stuckCutoff, DateTimeOffset deliveredSince, CancellationToken cancellationToken = default)
+    {
+        var now = DateTimeOffset.UtcNow;
+
+        var queueDepth = await CountBySiteAsync(
+            n => n.Status == NotificationStatus.Pending || n.Status == NotificationStatus.Retrying,
+            cancellationToken);
+
+        var stuck = await CountBySiteAsync(
+            n => (n.Status == NotificationStatus.Pending || n.Status == NotificationStatus.Retrying)
+                && n.CreatedAt < stuckCutoff,
+            cancellationToken);
+
+        var parked = await CountBySiteAsync(
+            n => n.Status == NotificationStatus.Parked, cancellationToken);
+
+        var delivered = await CountBySiteAsync(
+            n => n.Status == NotificationStatus.Delivered
+                && n.DeliveredAt != null && n.DeliveredAt >= deliveredSince,
+            cancellationToken);
+
+        // Oldest non-terminal CreatedAt per site. A SQL Min over the DateTimeOffset
+        // converter is awkward (see ComputeKpisAsync), so project the non-terminal
+        // (site, created) pairs — the live queue, which stays bounded — and reduce
+        // in memory.
+        var oldest = (await _context.Notifications
+                .Where(n => n.Status == NotificationStatus.Pending
+                    || n.Status == NotificationStatus.Retrying)
+                .Select(n => new { n.SourceSiteId, n.CreatedAt })
+                .ToListAsync(cancellationToken))
+            .GroupBy(x => x.SourceSiteId)
+            .ToDictionary(g => g.Key, g => g.Min(x => x.CreatedAt));
+
+        var siteIds = queueDepth.Keys
+            .Concat(stuck.Keys).Concat(parked.Keys).Concat(delivered.Keys)
+            .Distinct()
+            .OrderBy(s => s, StringComparer.Ordinal);
+
+        return siteIds.Select(site => new SiteNotificationKpiSnapshot(
+            SourceSiteId: site,
+            QueueDepth: queueDepth.GetValueOrDefault(site),
+            StuckCount: stuck.GetValueOrDefault(site),
+            ParkedCount: parked.GetValueOrDefault(site),
+            DeliveredLastInterval: delivered.GetValueOrDefault(site),
+            OldestPendingAge: oldest.TryGetValue(site, out var createdAt)
+                ? now - createdAt
+                : null)).ToList();
+    }
+
+    /// <summary>Counts notification rows matching <paramref name="predicate"/>, grouped by source site.</summary>
+    private async Task<Dictionary<string, int>> CountBySiteAsync(
+        System.Linq.Expressions.Expression<Func<Notification, bool>> predicate,
+        CancellationToken cancellationToken)
+    {
+        return await _context.Notifications
+            .Where(predicate)
+            .GroupBy(n => n.SourceSiteId)
+            .Select(g => new { Site = g.Key, Count = g.Count() })
+            .ToDictionaryAsync(x => x.Site, x => x.Count, cancellationToken);
+    }
+
     public async Task<int> SaveChangesAsync(CancellationToken cancellationToken = default)
         => await _context.SaveChangesAsync(cancellationToken);
 }
diff --git a/tests/ScadaLink.ConfigurationDatabase.Tests/NotificationOutboxRepositoryPerSiteKpiTests.cs b/tests/ScadaLink.ConfigurationDatabase.Tests/NotificationOutboxRepositoryPerSiteKpiTests.cs
new file mode 100644
index 0000000..299a447
--- /dev/null
+++ b/tests/ScadaLink.ConfigurationDatabase.Tests/NotificationOutboxRepositoryPerSiteKpiTests.cs
@@ -0,0 +1,70 @@
+using Microsoft.EntityFrameworkCore;
+using ScadaLink.Commons.Entities.Notifications;
+using ScadaLink.Commons.Types.Enums;
+using ScadaLink.ConfigurationDatabase;
+using ScadaLink.ConfigurationDatabase.Repositories;
+
+namespace ScadaLink.ConfigurationDatabase.Tests;
+
+// Coverage for per-site KPI aggregation in the Notification Outbox repository
+// (Task 2 of the notifications-nav-group feature).
+public class NotificationOutboxRepositoryPerSiteKpiTests
+{
+    private static ScadaLinkDbContext NewContext() => SqliteTestHelper.CreateInMemoryContext();
+
+    private static Notification NewNotification(
+        string sourceSiteId,
+        NotificationStatus status,
+        DateTimeOffset createdAt,
+        DateTimeOffset? deliveredAt = null)
+    {
+        return new Notification(
+            Guid.NewGuid().ToString(), NotificationType.Email, "Ops List", "Subject", "Body", sourceSiteId)
+        {
+            Status = status,
+            CreatedAt = createdAt,
+            DeliveredAt = deliveredAt,
+        };
+    }
+
+    [Fact]
+    public async Task ComputePerSiteKpisAsync_AggregatesMetricsPerSite()
+    {
+        await using var ctx = NewContext();
+        var now = DateTimeOffset.UtcNow;
+
+        // plant-a: 1 pending (stuck, created 20m ago), 1 parked
+        ctx.Notifications.Add(NewNotification("plant-a", NotificationStatus.Pending, createdAt: now.AddMinutes(-20)));
+        ctx.Notifications.Add(NewNotification("plant-a", NotificationStatus.Parked, createdAt: now.AddMinutes(-5)));
+        // plant-b: 1 delivered in-window, 1 pending (fresh)
+        ctx.Notifications.Add(NewNotification("plant-b", NotificationStatus.Delivered, createdAt: now.AddHours(-2), deliveredAt: now.AddMinutes(-2)));
+        ctx.Notifications.Add(NewNotification("plant-b", NotificationStatus.Pending, createdAt: now.AddMinutes(-1)));
+        await ctx.SaveChangesAsync();
+
+        var repo = new NotificationOutboxRepository(ctx);
+        var result = await repo.ComputePerSiteKpisAsync(
+            stuckCutoff: now.AddMinutes(-10), deliveredSince: now.AddMinutes(-30));
+
+        var a = result.Single(s => s.SourceSiteId == "plant-a");
+        Assert.Equal(1, a.QueueDepth);
+        Assert.Equal(1, a.StuckCount);
+        Assert.Equal(1, a.ParkedCount);
+        Assert.Equal(0, a.DeliveredLastInterval);
+        Assert.NotNull(a.OldestPendingAge);
+
+        var b = result.Single(s => s.SourceSiteId == "plant-b");
+        Assert.Equal(1, b.QueueDepth);
+        Assert.Equal(0, b.StuckCount);
+        Assert.Equal(1, b.DeliveredLastInterval);
+    }
+
+    [Fact]
+    public async Task ComputePerSiteKpisAsync_ReturnsEmpty_WhenNoNotifications()
+    {
+        await using var ctx = NewContext();
+        var repo = new NotificationOutboxRepository(ctx);
+        var result = await repo.ComputePerSiteKpisAsync(
+            DateTimeOffset.UtcNow, DateTimeOffset.UtcNow.AddMinutes(-30));
+        Assert.Empty(result);
+    }
+}