diff --git a/containers/libreportal/frontend/js/components/admin/system-metric-page.js b/containers/libreportal/frontend/js/components/admin/system-metric-page.js
index 4da23d0..f6518dc 100644
--- a/containers/libreportal/frontend/js/components/admin/system-metric-page.js
+++ b/containers/libreportal/frontend/js/components/admin/system-metric-page.js
@@ -211,9 +211,18 @@ class SystemMetricPage {
         }
     }
 
+    // Plain-language description of what the page shows, per metric.
     _subline() {
-        // Stub — populated more fully once data lands (sample count + tier).
-        return 'Live · binary ring backed';
+        const descs = {
+            cpu:    'Processor load over time, across all cores.',
+            mem:    'Memory in use over time, as a share of total RAM.',
+            swap:   'Swap in use over time, as a share of total swap.',
+            disk:   'Root-filesystem usage over time.',
+            load1:  'System load average (1-minute) over time.',
+            net_rx: 'Inbound network throughput over time.',
+            net_tx: 'Outbound network throughput over time.',
+        };
+        return (this.metric && descs[this.metric.key]) || 'Live history over time.';
     }
 
     async _loadRange() {