diff --git a/docs/configuration/template_reference.md b/docs/configuration/template_reference.md
index 92161f4c6..67e37e0d3 100644
--- a/docs/configuration/template_reference.md
+++ b/docs/configuration/template_reference.md
@@ -90,9 +90,9 @@ parameterize templates, and have a few other differences.
 
 ### Alert field templates
 
-`.Value`, `.Labels`, and `.ExternalLabels` contain the alert value, the alert
-labels, and the globally configured external labels, respectively. They are
-also exposed as the `$value`, `$labels`, and `$externalLabels` variables for
+`.Value`, `.Labels`, `.ExternalLabels`, and `.ExternalURL` contain the alert value, the alert
+labels, the globally configured external labels, and the external URL (configured with `--web.external-url`) respectively. They are
+also exposed as the `$value`, `$labels`, `$externalLabels`, and `$externalURL` variables for
 convenience.
 
 ### Console templates
diff --git a/docs/configuration/unit_testing_rules.md b/docs/configuration/unit_testing_rules.md
index 644b35a17..1cf87d6b3 100644
--- a/docs/configuration/unit_testing_rules.md
+++ b/docs/configuration/unit_testing_rules.md
@@ -59,6 +59,10 @@ promql_expr_test:
 # External labels accessible to the alert template.
 external_labels:
   [ <labelname>: <string> ... ]
+
+# External URL accessible to the alert template.
+# Usually set using --web.external-url.
+  [ external_url: <string> ]
 ```
 
 ### `<series>`