diff --git a/docs/en/setup/backend/backend-alarm.md b/docs/en/setup/backend/backend-alarm.md
index 72ed924dd..c1080d88d 100644
--- a/docs/en/setup/backend/backend-alarm.md
+++ b/docs/en/setup/backend/backend-alarm.md
@@ -1,6 +1,6 @@
 # Alarm
 Alarm core is driven by a collection of rules, which are defined in `config/alarm-settings.yml`.
-There are two parts in alarm rule definition.
+There are three parts in alarm rule definition.
 1. [Alarm rules](#rules). They define how metrics alarm should be triggered, what conditions should be considered.
 1. [Webhooks](#webhook). The list of web service endpoint, which should be called after the alarm is triggered.
 1. [gRPCHook](#gRPCHook). The host and port of remote gRPC method, which should be called after the alarm is triggered.
@@ -138,4 +138,4 @@ which will override the settings in `alarm-settings.yml`.
 
 In order to determine that whether an alarm rule is triggered or not, SkyWalking needs to cache the metrics of a time window for
 each alarm rule, if any attribute (`metrics-name`, `op`, `threshold`, `period`, `count`, etc.) of a rule is changed,
-the sliding window will be destroyed and re-created, causing the alarm of this specific rule to restart again.
\ No newline at end of file
+the sliding window will be destroyed and re-created, causing the alarm of this specific rule to restart again.