- The Alertmanager uses labels to match alerts for [silences]({{< relref "../../silences/" >}}) and [alert groups]({{< relref "../../alert-groups/" >}}) in [notification policies]({{< relref "../../notifications/" >}}).
- The alerting UI shows labels for every alert instance generated during evaluation of that rule.
- Contact points can access labels to dynamically generate notifications that contain information specific to the alert that is resulting in a notification.
- You can add labels to an [alerting rule]({{< relref "../../alerting-rules/" >}}). Labels are manually configurable, use template functions, and can reference other labels. Labels added to an alerting rule take precedence in the event of a collision between labels (except in the case of [Grafana reserved labels](#grafana-reserved-labels)).
Grafana's built-in Alertmanager supports both Unicode label keys and values. If you are using an external Prometheus Alertmanager, label keys must be compatible with their [data model](https://prometheus.io/docs/concepts/data_model/#metric-names-and-labels).
This means that label keys must only contain **ASCII letters**, **numbers**, as well as **underscores** and match the regex `[a-zA-Z_][a-zA-Z0-9_]*`.
Any invalid characters will be removed or replaced by the Grafana alerting engine before being sent to the external Alertmanager according to the following rules:
-`Whitespace` will be removed.
-`ASCII characters` will be replaced with `_`.
-`All other characters` will be replaced with their lower-case hex representation. If this is the first character it will be prefixed with `_`.
Example: A label key/value pair `Alert! 🔔="🔥"` will become `Alert_0x1f514="🔥"`.
**Note** If multiple label keys are sanitized to the same value, the duplicates will have a short hash of the original label appended as a suffix.
> **Note:** Labels prefixed with `grafana_` are reserved by Grafana for special use. If a manually configured label is added beginning with `grafana_` it may be overwritten in case of collision.
> To stop the Grafana Alerting engine from adding a reserved label, you can disable it via the `disabled_labels` option in [unified_alerting.reserved_labels]({{< relref "../../../setup-grafana/configure-grafana/#unified_alertingreserved_labels" >}}) configuration.
