diff --git a/monitoring/metrics.html.md b/monitoring/metrics.html.md
index 2b460b9095..0961eb30b9 100644
--- a/monitoring/metrics.html.md
+++ b/monitoring/metrics.html.md
@@ -92,6 +92,17 @@ curl https://api.fly.io/prometheus/$ORG_SLUG/api/v1/query \
   -H "Authorization: Bearer $TOKEN"
 ```
 
+## Retention, cost, and limits
+
+Prometheus on Fly.io retains metric data for approximately 15 days and is intended for operational monitoring. If you need longer retention, run your own monitoring stack. Fly.io's [Observability for User Apps](/docs/blueprints/observability-for-user-apps/) guide deploys a ready-made stack, or you can federate from the Fly.io endpoint into your own Prometheus installation.
+
+There's currently no additional charge for the managed Prometheus and Grafana. Pricing could change in the future, and Fly.io will give advance notice.
+
+A couple of practical limits to be aware of:
+
+- We cap your app's metrics endpoint response at 16 KiB and drop anything larger.
+- We may drop very high-cardinality custom metrics.
+
 ## Dashboards
 
 For more advanced metrics monitoring, you can use dashboards to organize and visualize complex Prometheus
@@ -132,6 +143,15 @@ We publish our [Fly.io Dashboards](https://grafana.com/grafana/dashboards/14741)
 To install, just [import the dashboard](https://grafana.com/docs/grafana/latest/dashboards/export-import/#import-dashboard) using the listed IDs.
 If you'd like to contribute changes to the dashboards, we have created a [repository](https://github.com/superfly/dashboards) for them.
 
+## Alerting
+
+Fly.io doesn't include built-in alerting on metrics, so you'll need to set up alerting yourself against the Prometheus endpoint. Two common approaches:
+
+- **Grafana alerting**: connect the Fly.io Prometheus data source to a Grafana instance (see the [External or self-hosted Grafana](#external-or-self-hosted-grafana) section), then create [Grafana alert rules](https://grafana.com/docs/grafana/latest/alerting/) on queries against the data source and send the alerts to a contact point such as email, Slack, or PagerDuty.
+- **Prometheus and Alertmanager**: run your own [Prometheus](https://prometheus.io/) that federates from the Fly.io endpoint and use [Alertmanager](https://prometheus.io/docs/alerting/latest/alertmanager/) to send notifications.
+
+If you don't already run Grafana or Prometheus, Fly.io's [Observability for User Apps](/docs/blueprints/observability-for-user-apps/) guide deploys a ready-made stack (VictoriaMetrics and Grafana) you can build alerts on.
+
 ## Built-in metrics
 
 Fly apps automatically publish a number of built-in metrics.