diff --git a/apps/emqx/etc/emqx.conf b/apps/emqx/etc/emqx.conf
index 63ec0f664..a272a110f 100644
--- a/apps/emqx/etc/emqx.conf
+++ b/apps/emqx/etc/emqx.conf
@@ -936,7 +936,7 @@ rate_limit {
   ##   max_conn_rate: 1000
   max_conn_rate = 1000
 
-  ## Message limit for the a external MQTT connection.
+  ## Message limit for the external MQTT connections.
   ##
   ## @doc rate_limit.conn_messages_in
   ## ValueType: String | infinity
diff --git a/apps/emqx/src/emqx_schema.erl b/apps/emqx/src/emqx_schema.erl
index 862bc3e76..2879d251d 100644
--- a/apps/emqx/src/emqx_schema.erl
+++ b/apps/emqx/src/emqx_schema.erl
@@ -623,17 +623,28 @@ fields("rate_limit") ->
         {"max_conn_rate",
             sc(
                 hoconsc:union([infinity, integer()]),
-                #{default => 1000}
+                #{
+                    default => 1000,
+                    desc => "Maximum connections per second."
+                }
             )},
         {"conn_messages_in",
             sc(
                 hoconsc:union([infinity, comma_separated_list()]),
-                #{default => infinity}
+                #{
+                    default => infinity,
+                    desc => "Message limit for the external MQTT connections."
+                }
             )},
         {"conn_bytes_in",
             sc(
                 hoconsc:union([infinity, comma_separated_list()]),
-                #{default => infinity}
+                #{
+                    default => infinity,
+                    desc =>
+                        "Limit the rate of receiving packets for a MQTT connection.\n"
+                        "The rate is counted by bytes of packets per second."
+                }
             )}
     ];
 fields("flapping_detect") ->