diff --git a/src/ZB.MOM.WW.ScadaBridge.AuditLog/Kpi/AuditLogKpiSampleSource.cs b/src/ZB.MOM.WW.ScadaBridge.AuditLog/Kpi/AuditLogKpiSampleSource.cs
index 5e69d58f..4e77a18d 100644
--- a/src/ZB.MOM.WW.ScadaBridge.AuditLog/Kpi/AuditLogKpiSampleSource.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.AuditLog/Kpi/AuditLogKpiSampleSource.cs
@@ -36,11 +36,12 @@ public sealed class AuditLogKpiSampleSource : IKpiSampleSource
     /// </summary>
     private static readonly TimeSpan Window = TimeSpan.FromHours(1);
 
-    // Metric catalog — the exact strings persisted in KpiSample.Metric. Stable
-    // identifiers the recorder + UI trend charts key on; do not rename.
-    private const string TotalEventsLastHourMetric = "totalEventsLastHour";
-    private const string ErrorEventsLastHourMetric = "errorEventsLastHour";
-    private const string BacklogTotalMetric = "backlogTotal";
+    // Metric catalog — the exact strings persisted in KpiSample.Metric. All three are
+    // charted, so they share the public Commons catalog: source + UI trend page key off
+    // one symbol (#178). Stable identifiers; do not rename (values are persisted).
+    private const string TotalEventsLastHourMetric = KpiMetrics.AuditLog.TotalEventsLastHour;
+    private const string ErrorEventsLastHourMetric = KpiMetrics.AuditLog.ErrorEventsLastHour;
+    private const string BacklogTotalMetric = KpiMetrics.AuditLog.BacklogTotal;
 
     private readonly IAuditLogRepository _repository;
 
diff --git a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Audit/AuditLogPage.razor.cs b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Audit/AuditLogPage.razor.cs
index 17e69792..1656a05f 100644
--- a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Audit/AuditLogPage.razor.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Audit/AuditLogPage.razor.cs
@@ -293,9 +293,9 @@ public partial class AuditLogPage : IDisposable
     /// <summary>The metrics rendered in the panel, in display order.</summary>
     private static readonly (string Metric, string Title, string? Unit)[] TrendMetrics =
     {
-        ("totalEventsLastHour", "Events / hour", null),
-        ("errorEventsLastHour", "Error events / hour", null),
-        ("backlogTotal", "Backlog", null),
+        (KpiMetrics.AuditLog.TotalEventsLastHour, "Events / hour", null),
+        (KpiMetrics.AuditLog.ErrorEventsLastHour, "Error events / hour", null),
+        (KpiMetrics.AuditLog.BacklogTotal, "Backlog", null),
     };
 
     /// <summary>Per-metric series state, keyed by the metric name.</summary>
diff --git a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Monitoring/Health.razor b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Monitoring/Health.razor
index a2381855..b71bfda1 100644
--- a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Monitoring/Health.razor
+++ b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Monitoring/Health.razor
@@ -593,13 +593,13 @@
             var siteId = _trendSiteId;
 
             (_connectionsDownSeries, _connectionsDownAvailable, _connectionsDownError) =
-                await LoadTrendSeriesAsync("connectionsDown", siteId, fromUtc, toUtc);
+                await LoadTrendSeriesAsync(KpiMetrics.SiteHealth.ConnectionsDown, siteId, fromUtc, toUtc);
             (_deadLettersSeries, _deadLettersAvailable, _deadLettersError) =
-                await LoadTrendSeriesAsync("deadLetters", siteId, fromUtc, toUtc);
+                await LoadTrendSeriesAsync(KpiMetrics.SiteHealth.DeadLetters, siteId, fromUtc, toUtc);
             (_scriptErrorsSeries, _scriptErrorsAvailable, _scriptErrorsError) =
-                await LoadTrendSeriesAsync("scriptErrors", siteId, fromUtc, toUtc);
+                await LoadTrendSeriesAsync(KpiMetrics.SiteHealth.ScriptErrors, siteId, fromUtc, toUtc);
             (_sfBufferDepthSeries, _sfBufferDepthAvailable, _sfBufferDepthError) =
-                await LoadTrendSeriesAsync("sfBufferDepth", siteId, fromUtc, toUtc);
+                await LoadTrendSeriesAsync(KpiMetrics.SiteHealth.SfBufferDepth, siteId, fromUtc, toUtc);
         }
         finally
         {
diff --git a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Notifications/NotificationKpis.razor b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Notifications/NotificationKpis.razor
index e2032706..f87c7747 100644
--- a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Notifications/NotificationKpis.razor
+++ b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Notifications/NotificationKpis.razor
@@ -279,11 +279,11 @@
             // one metric's failure only blanks that one chart while the others still
             // render their fetched data — and a throw never breaks the KPI tiles above.
             (_queueDepthSeries, _queueDepthAvailable, _queueDepthError) =
-                await LoadSeries("queueDepth", fromUtc, toUtc);
+                await LoadSeries(KpiMetrics.NotificationOutbox.QueueDepth, fromUtc, toUtc);
             (_parkedSeries, _parkedAvailable, _parkedError) =
-                await LoadSeries("parkedCount", fromUtc, toUtc);
+                await LoadSeries(KpiMetrics.NotificationOutbox.ParkedCount, fromUtc, toUtc);
             (_deliveredSeries, _deliveredAvailable, _deliveredError) =
-                await LoadSeries("deliveredLastInterval", fromUtc, toUtc);
+                await LoadSeries(KpiMetrics.NotificationOutbox.DeliveredLastInterval, fromUtc, toUtc);
         }
         finally
         {
diff --git a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/SiteCalls/SiteCallsReport.razor.cs b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/SiteCalls/SiteCallsReport.razor.cs
index 742bfde5..69c14e95 100644
--- a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/SiteCalls/SiteCallsReport.razor.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/SiteCalls/SiteCallsReport.razor.cs
@@ -591,11 +591,11 @@ public partial class SiteCallsReport
             var fromUtc = toUtc - TimeSpan.FromHours(_windowHours);
 
             (_bufferedSeries, _bufferedAvailable, _bufferedError) =
-                await LoadSeriesAsync("buffered", fromUtc, toUtc);
+                await LoadSeriesAsync(KpiMetrics.SiteCallAudit.Buffered, fromUtc, toUtc);
             (_parkedSeries, _parkedAvailable, _parkedError) =
-                await LoadSeriesAsync("parked", fromUtc, toUtc);
+                await LoadSeriesAsync(KpiMetrics.SiteCallAudit.Parked, fromUtc, toUtc);
             (_failedSeries, _failedAvailable, _failedError) =
-                await LoadSeriesAsync("failedLastInterval", fromUtc, toUtc);
+                await LoadSeriesAsync(KpiMetrics.SiteCallAudit.FailedLastInterval, fromUtc, toUtc);
         }
         finally
         {
diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Kpi/KpiMetrics.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Kpi/KpiMetrics.cs
new file mode 100644
index 00000000..6ceff384
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Kpi/KpiMetrics.cs
@@ -0,0 +1,98 @@
+namespace ZB.MOM.WW.ScadaBridge.Commons.Types.Kpi;
+
+/// <summary>
+/// Canonical <em>charted</em> KPI metric-name identifiers (M6 "KPI History &amp;
+/// Trends") — the value of <see cref="ZB.MOM.WW.ScadaBridge.Commons.Entities.Kpi.KpiSample.Metric"/>
+/// for every metric a Central UI trend chart renders. Each owning
+/// <see cref="ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Kpi.IKpiSampleSource"/> emits
+/// these strings and each trend page keys its <c>GetSeriesAsync</c> lookup on the same
+/// strings; promoting them to one shared public symbol means the source and the page key
+/// off a single declaration, so a future rename becomes a compiler-enforced single edit
+/// rather than a silently-blanked chart.
+/// </summary>
+/// <remarks>
+/// <para>
+/// Each constant's value is the metric string <em>as persisted</em> in the tall/EAV
+/// <c>KpiSample</c> table and matched at query time. These values are therefore part of
+/// the on-disk data contract: this catalog is a symbol-promotion of the existing literals,
+/// <strong>not</strong> a rename — changing any value would orphan historical samples.
+/// </para>
+/// <para>
+/// Only the metrics a trend page actually charts are catalogued here. Sources may emit
+/// additional internal metrics (e.g. the Notification Outbox <c>stuckCount</c> /
+/// <c>oldestPendingAgeSeconds</c>, the Site Call Audit <c>deliveredLastInterval</c> /
+/// <c>stuck</c> / <c>oldestPendingAgeSeconds</c>, and the bulk of the Site Health catalog)
+/// that no page references; those stay private to their source until a page charts them.
+/// Constants are grouped by source via nested static classes mirroring
+/// <see cref="KpiSources"/>.
+/// </para>
+/// </remarks>
+public static class KpiMetrics
+{
+    /// <summary>
+    /// Charted Notification Outbox (#21) metrics — <see cref="KpiSources.NotificationOutbox"/>.
+    /// Rendered by the Central UI Notification Outbox KPIs trend panel.
+    /// </summary>
+    public static class NotificationOutbox
+    {
+        /// <summary>Pending-queue depth (rows awaiting delivery).</summary>
+        public const string QueueDepth = "queueDepth";
+
+        /// <summary>Parked-row count.</summary>
+        public const string ParkedCount = "parkedCount";
+
+        /// <summary>Rows delivered in the last KPI interval.</summary>
+        public const string DeliveredLastInterval = "deliveredLastInterval";
+    }
+
+    /// <summary>
+    /// Charted Site Call Audit (#22) metrics — <see cref="KpiSources.SiteCallAudit"/>.
+    /// Rendered by the Central UI Site Calls report trend panel.
+    /// </summary>
+    public static class SiteCallAudit
+    {
+        /// <summary>Buffered (non-terminal) cached-call count.</summary>
+        public const string Buffered = "buffered";
+
+        /// <summary>Parked cached-call count.</summary>
+        public const string Parked = "parked";
+
+        /// <summary>Cached calls that failed permanently in the last KPI interval.</summary>
+        public const string FailedLastInterval = "failedLastInterval";
+    }
+
+    /// <summary>
+    /// Charted Audit Log (#23) metrics — <see cref="KpiSources.AuditLog"/>.
+    /// Rendered by the Central UI Audit Log page trend panel.
+    /// </summary>
+    public static class AuditLog
+    {
+        /// <summary>Audit events recorded in the trailing hour.</summary>
+        public const string TotalEventsLastHour = "totalEventsLastHour";
+
+        /// <summary>Error-row audit events recorded in the trailing hour.</summary>
+        public const string ErrorEventsLastHour = "errorEventsLastHour";
+
+        /// <summary>Total pending (not-yet-forwarded) audit backlog.</summary>
+        public const string BacklogTotal = "backlogTotal";
+    }
+
+    /// <summary>
+    /// Charted Site Health (#11) metrics — <see cref="KpiSources.SiteHealth"/>.
+    /// Rendered by the Central UI Health-dashboard per-site trend panel.
+    /// </summary>
+    public static class SiteHealth
+    {
+        /// <summary>Data connections not in the Connected state.</summary>
+        public const string ConnectionsDown = "connectionsDown";
+
+        /// <summary>Dead-letter count reported by the site.</summary>
+        public const string DeadLetters = "deadLetters";
+
+        /// <summary>Script-execution error count reported by the site.</summary>
+        public const string ScriptErrors = "scriptErrors";
+
+        /// <summary>Summed store-and-forward buffer depth across all buffers.</summary>
+        public const string SfBufferDepth = "sfBufferDepth";
+    }
+}
diff --git a/src/ZB.MOM.WW.ScadaBridge.HealthMonitoring/Kpi/SiteHealthKpiSampleSource.cs b/src/ZB.MOM.WW.ScadaBridge.HealthMonitoring/Kpi/SiteHealthKpiSampleSource.cs
index 0ae3ae4b..2ef5a2a4 100644
--- a/src/ZB.MOM.WW.ScadaBridge.HealthMonitoring/Kpi/SiteHealthKpiSampleSource.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.HealthMonitoring/Kpi/SiteHealthKpiSampleSource.cs
@@ -34,13 +34,15 @@ namespace ZB.MOM.WW.ScadaBridge.HealthMonitoring.Kpi;
 public sealed class SiteHealthKpiSampleSource : IKpiSampleSource
 {
     // ── Metric catalog (the M6-agreed metric-name strings for this source) ──
-    // Declaration order matches the emission order in AddSiteSnapshot.
+    // Declaration order matches the emission order in AddSiteSnapshot. Charted metrics
+    // share the public Commons catalog so source + UI trend page key off one symbol
+    // (#178); the uncharted internal metrics stay private here.
     private const string MetricConnectionsUp = "connectionsUp";
-    private const string MetricConnectionsDown = "connectionsDown";
-    private const string MetricScriptErrors = "scriptErrors";
+    private const string MetricConnectionsDown = KpiMetrics.SiteHealth.ConnectionsDown;
+    private const string MetricScriptErrors = KpiMetrics.SiteHealth.ScriptErrors;
     private const string MetricAlarmEvalErrors = "alarmEvalErrors";
-    private const string MetricSfBufferDepth = "sfBufferDepth";
-    private const string MetricDeadLetters = "deadLetters";
+    private const string MetricSfBufferDepth = KpiMetrics.SiteHealth.SfBufferDepth;
+    private const string MetricDeadLetters = KpiMetrics.SiteHealth.DeadLetters;
     private const string MetricParkedMessages = "parkedMessages";
     private const string MetricDeployedInstances = "deployedInstances";
     private const string MetricEnabledInstances = "enabledInstances";
diff --git a/src/ZB.MOM.WW.ScadaBridge.NotificationOutbox/Kpi/NotificationOutboxKpiSampleSource.cs b/src/ZB.MOM.WW.ScadaBridge.NotificationOutbox/Kpi/NotificationOutboxKpiSampleSource.cs
index e0b0174b..07dc6246 100644
--- a/src/ZB.MOM.WW.ScadaBridge.NotificationOutbox/Kpi/NotificationOutboxKpiSampleSource.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.NotificationOutbox/Kpi/NotificationOutboxKpiSampleSource.cs
@@ -34,10 +34,12 @@ namespace ZB.MOM.WW.ScadaBridge.NotificationOutbox.Kpi;
 /// </remarks>
 public sealed class NotificationOutboxKpiSampleSource : IKpiSampleSource
 {
-    private const string MetricQueueDepth = "queueDepth";
+    // Charted metrics share the public Commons catalog so source + UI trend page key
+    // off one symbol (#178). The uncharted internal metrics stay private here.
+    private const string MetricQueueDepth = KpiMetrics.NotificationOutbox.QueueDepth;
     private const string MetricStuckCount = "stuckCount";
-    private const string MetricParkedCount = "parkedCount";
-    private const string MetricDeliveredLastInterval = "deliveredLastInterval";
+    private const string MetricParkedCount = KpiMetrics.NotificationOutbox.ParkedCount;
+    private const string MetricDeliveredLastInterval = KpiMetrics.NotificationOutbox.DeliveredLastInterval;
     private const string MetricOldestPendingAgeSeconds = "oldestPendingAgeSeconds";
 
     private readonly INotificationOutboxRepository _repository;
diff --git a/src/ZB.MOM.WW.ScadaBridge.SiteCallAudit/Kpi/SiteCallAuditKpiSampleSource.cs b/src/ZB.MOM.WW.ScadaBridge.SiteCallAudit/Kpi/SiteCallAuditKpiSampleSource.cs
index 3accce76..93b59a4a 100644
--- a/src/ZB.MOM.WW.ScadaBridge.SiteCallAudit/Kpi/SiteCallAuditKpiSampleSource.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.SiteCallAudit/Kpi/SiteCallAuditKpiSampleSource.cs
@@ -36,10 +36,12 @@ namespace ZB.MOM.WW.ScadaBridge.SiteCallAudit.Kpi;
 public sealed class SiteCallAuditKpiSampleSource : IKpiSampleSource
 {
     // ── Metric catalog (the M6-agreed metric-name strings for this source) ──
-    // Declaration order matches the emission order in AddSnapshot.
-    private const string MetricBuffered = "buffered";
-    private const string MetricParked = "parked";
-    private const string MetricFailedLastInterval = "failedLastInterval";
+    // Declaration order matches the emission order in AddSnapshot. Charted metrics
+    // share the public Commons catalog so source + UI trend page key off one symbol
+    // (#178); the uncharted internal metrics stay private here.
+    private const string MetricBuffered = KpiMetrics.SiteCallAudit.Buffered;
+    private const string MetricParked = KpiMetrics.SiteCallAudit.Parked;
+    private const string MetricFailedLastInterval = KpiMetrics.SiteCallAudit.FailedLastInterval;
     private const string MetricDeliveredLastInterval = "deliveredLastInterval";
     private const string MetricStuck = "stuck";
     private const string MetricOldestPendingAgeSeconds = "oldestPendingAgeSeconds";