diff --git a/apps/emqx_gateway/src/emqx_gateway_schema.erl b/apps/emqx_gateway/src/emqx_gateway_schema.erl
index 9a28e5e0d..b793bcf37 100644
--- a/apps/emqx_gateway/src/emqx_gateway_schema.erl
+++ b/apps/emqx_gateway/src/emqx_gateway_schema.erl
@@ -53,11 +53,26 @@ namespace() -> gateway.
 roots() -> [gateway].
 
 fields(gateway) ->
-    [{stomp,   sc_meta(ref(stomp)  , #{nullable => {true, recursively}})},
-     {mqttsn,  sc_meta(ref(mqttsn) , #{nullable => {true, recursively}})},
-     {coap,    sc_meta(ref(coap)   , #{nullable => {true, recursively}})},
-     {lwm2m,   sc_meta(ref(lwm2m)  , #{nullable => {true, recursively}})},
-     {exproto, sc_meta(ref(exproto), #{nullable => {true, recursively}})}
+    [{stomp,   sc(ref(stomp),
+                  #{ nullable => {true, recursively}
+                   , desc => "The Stomp Gateway configuration."
+                   })},
+     {mqttsn,  sc(ref(mqttsn),
+                  #{ nullable => {true, recursively}
+                   , desc => "The MQTT-SN Gateway configuration"
+                   })},
+     {coap,    sc(ref(coap),
+                  #{ nullable => {true, recursively}
+                   , desc => "The CoAP Gateway configuration"
+                   })},
+     {lwm2m,   sc(ref(lwm2m),
+                  #{ nullable => {true, recursively}
+                   , desc => "The LwM2M Gateway configuration"
+                   })},
+     {exproto, sc(ref(exproto),
+                  #{ nullable => {true, recursively}
+                   , desc => "The Extension Protocol configuration"
+                   })}
     ];
 
 fields(stomp) ->
@@ -66,61 +81,198 @@ fields(stomp) ->
     ] ++ gateway_common_options();
 
 fields(stomp_frame) ->
-    [ {max_headers, sc(integer(), 10)}
-    , {max_headers_length, sc(integer(), 1024)}
-    , {max_body_length, sc(integer(), 8192)}
+    [ {max_headers,
+       sc(integer(),
+          #{ default => 10
+           , desc => "The maximum number of Header"
+           })}
+    , {max_headers_length,
+       sc(integer(),
+          #{ default => 1024
+           , desc => "The maximum string length of the Header Value"
+           })}
+    , {max_body_length,
+       sc(integer(),
+          #{ default => 65536
+           , desc => "Maximum number of bytes of Body allowed per Stomp packet"
+           })}
     ];
 
 fields(mqttsn) ->
-    [ {gateway_id, sc(integer())}
-    , {broadcast, sc(boolean(), false)}
-    , {enable_qos3, sc(boolean(), true)}
-    , {predefined, hoconsc:array(ref(mqttsn_predefined))}
+    [ {gateway_id,
+       sc(integer(),
+          #{ default => 1
+           , desc =>
+"MQTT-SN Gateway Id.<br>
+When the <code>broadcast</code> option is enabled,
+the gateway will broadcast ADVERTISE message with this value"
+           })}
+    , {broadcast,
+       sc(boolean(),
+          #{ default => false
+           , desc => "Whether to periodically broadcast ADVERTISE messages"
+           })}
+    %% TODO: rename
+    , {enable_qos3,
+       sc(boolean(),
+          #{ default => true
+           , desc =>
+"Allows connectionless clients to publish messages with a Qos of -1.<br>
+This feature is defined for very simple client implementations
+which do not support any other features except this one.<br>
+There is no connection setup nor tear down, no registration nor subscription.<br>
+The client just sends its PUBLISH messages to a GW"
+           })}
+    , {predefined,
+       sc(hoconsc:array(ref(mqttsn_predefined)),
+          #{ default => []
+           , desc =>
+"The Pre-defined topic ids and topic names.<br>
+A 'pre-defined' topic id is a topic id whose mapping to a topic name
+is known in advance by both the client’s application and the gateway"
+           })}
     , {listeners, sc(ref(udp_listeners))}
     ] ++ gateway_common_options();
 
 fields(mqttsn_predefined) ->
-    [ {id, sc(integer())}
-    , {topic, sc(binary())}
+    [ {id, sc(integer(), #{desc => "Topic Id.<br>Range: 1-65535"})}
+    , {topic, sc(binary(), #{desc => "Topic Name"})}
     ];
 
 fields(coap) ->
-    [ {heartbeat, sc(duration(), <<"30s">>)}
-    , {connection_required, sc(boolean(), false)}
-    , {notify_type, sc(hoconsc:union([non, con, qos]), qos)}
-    , {subscribe_qos, sc(hoconsc:union([qos0, qos1, qos2, coap]), coap)}
-    , {publish_qos, sc(hoconsc:union([qos0, qos1, qos2, coap]), coap)}
+    [ {heartbeat,
+       sc(duration(),
+          #{ default => <<"30s">>
+           , desc =>
+"The gateway server required minimum hearbeat interval.<br>
+When connection mode is enabled, this parameter is used to set the minimum
+heartbeat interval for the connection to be alive."
+           })}
+    , {connection_required,
+       sc(boolean(),
+          #{ default => false
+           , desc =>
+"Enable or disable connection mode.<br>
+Connection mode is a feature of non-standard protocols. When connection mode
+is enabled, it is necessary to maintain the creation, authentication and alive
+of connection resources"
+           })}
+    , {notify_type,
+       sc(hoconsc:union([non, con, qos]),
+          #{ default => qos
+           , desc =>
+"The Notification Message will be delivered to the CoAP client if a new message
+received on an observed topic.
+The type of delivered coap message can be set to:<br>
+1. non: Non-confirmable;<br>
+2. con: Confirmable;<br>
+3. qos: Mapping from QoS type of recevied message, QoS0 -> non, QoS1,2 -> con"
+           })}
+    , {subscribe_qos,
+       sc(hoconsc:union([qos0, qos1, qos2, coap]),
+          #{ default => coap
+           , desc =>
+"The Default QoS Level indicator for subscribe request.<br>
+This option specifies the QoS level for the CoAP Client when establishing a
+subscription membership, if the subscribe request is not carried `qos` option.
+The indicator can be set to:
+  - qos0, qos1, qos2: Fixed default QoS level
+  - coap: Dynamic QoS level by the message type of subscribe request
+    * qos0: If the subscribe request is non-confirmable
+    * qos1: If the subscribe request is confirmable"
+           })}
+    , {publish_qos,
+       sc(hoconsc:union([qos0, qos1, qos2, coap]),
+          #{ default => coap
+           , desc =>
+"The Default QoS Level indicator for publish request.<br>
+This option specifies the QoS level for the CoAP Client when publishing a
+message to EMQ X PUB/SUB system, if the publish request is not carried `qos`
+option. The indicator can be set to:
+  - qos0, qos1, qos2: Fixed default QoS level
+  - coap: Dynamic QoS level by the message type of publish request
+    * qos0: If the publish request is non-confirmable
+    * qos1: If the publish request is confirmable"
+           })}
     , {listeners, sc(ref(udp_listeners))}
     ] ++ gateway_common_options();
 
 fields(lwm2m) ->
-    [ {xml_dir, sc(binary(), "etc/lwm2m_xml")}
-    , {lifetime_min, sc(duration(), "1s")}
-    , {lifetime_max, sc(duration(), "86400s")}
-    , {qmode_time_window, sc(duration_s(), "22s")}
+    [ {xml_dir,
+       sc(binary(),
+          #{ default =>"etc/lwm2m_xml"
+           , desc => "The Directory for LwM2M Resource defination"
+           })}
+    , {lifetime_min,
+       sc(duration(),
+          #{ default => "1s"
+           , desc => "Minimum value of lifetime allowed to be set by the LwM2M client"
+           })}
+    , {lifetime_max,
+       sc(duration(),
+          #{ default => "86400s"
+           , desc => "Maximum value of lifetime allowed to be set by the LwM2M client"
+           })}
+    , {qmode_time_window,
+       sc(duration_s(),
+          #{ default => "22s"
+           , desc =>
+"The value of the time window during which the network link is considered
+valid by the LwM2M Gateway in QMode mode.<br>
+For example, after receiving an update message from a client, any messages
+within this time window are sent directly to the LwM2M client, and all messages
+beyond this time window are temporarily stored in memory."
+           })}
     %% TODO: Support config resource path
-    , {auto_observe, sc(boolean(), false)}
-    , {update_msg_publish_condition, sc(hoconsc:union([always, contains_object_list]))}
-    , {translators, sc_meta(ref(translators), #{nullable => false})}
+    , {auto_observe,
+       sc(boolean(),
+          #{ default => false
+           , desc => "Automatically observe the object list of REGISTER packet"
+           })}
+    %% FIXME: not working now
+    , {update_msg_publish_condition,
+       sc(hoconsc:union([always, contains_object_list]),
+          #{ default => "contains_object_list"
+           , desc =>
+"Policy for publishing UPDATE event message to EMQ X.<br>
+  - always: send update events as long as the UPDATE request is received.
+  - contains_object_list: send update events only if the UPDATE request carries any Object List."
+           })}
+    , {translators,
+       sc(ref(lwm2m_translators),
+          #{ nullable => false
+           , desc => "Topic configuration for LwM2M's gateway publishing and subscription"
+           })}
     , {listeners, sc(ref(udp_listeners))}
     ] ++ gateway_common_options();
 
 fields(exproto) ->
-    [ {server, sc(ref(exproto_grpc_server))}
-    , {handler, sc(ref(exproto_grpc_handler))}
+    [ {server,
+       sc(ref(exproto_grpc_server),
+          #{ desc => "Configurations for starting the <code>ConnectionAdapter</code> service"
+           })}
+    , {handler,
+       sc(ref(exproto_grpc_handler),
+          #{ desc => "Configurations for request to <code>ConnectionHandler</code> service"
+           })}
     , {listeners, sc(ref(udp_tcp_listeners))}
     ] ++ gateway_common_options();
 
 fields(exproto_grpc_server) ->
-    [ {bind, sc(hoconsc:union([ip_port(), integer()]))}
-    , {ssl, sc_meta(ref(ssl_server_opts),
-                    #{nullable => {true, recursively}})}
+    [ {bind,
+       sc(hoconsc:union([ip_port(), integer()]))}
+    , {ssl,
+       sc(ref(ssl_server_opts),
+          #{ nullable => {true, recursively}
+           })}
     ];
 
 fields(exproto_grpc_handler) ->
     [ {address, sc(binary())}
-    , {ssl, sc_meta(ref(ssl_client_opts),
-                    #{nullable => {true, recursively}})}
+    , {ssl,
+       sc(ref(ssl_client_opts),
+          #{ nullable => {true, recursively}
+           })}
     ];
 
 fields(ssl_server_opts) ->
@@ -140,12 +292,36 @@ fields(clientinfo_override) ->
     , {clientid, sc(binary())}
     ];
 
-fields(translators) ->
-    [ {command, sc(ref(translator))}
-    , {response, sc(ref(translator))}
-    , {notify, sc(ref(translator))}
-    , {register, sc(ref(translator))}
-    , {update, sc(ref(translator))}
+fields(lwm2m_translators) ->
+    [ {command,
+       sc(ref(translator),
+          #{ desc =>
+"The topic for receiving downstream commands.<br>
+For each new LwM2M client that succeeds in going online, the gateway creates
+a the subscription relationship to receive downstream commands and send it to
+the LwM2M client"
+           })}
+    , {response,
+       sc(ref(translator),
+          #{ desc =>
+"The topic for gateway to publish the acknowledge events from LwM2M client"
+           })}
+    , {notify,
+       sc(ref(translator),
+          #{ desc =>
+"The topic for gateway to publish the notify events from LwM2M client.<br>
+After succeed observe a resource of LwM2M client, Gateway will send the notifyevents via this topic, if the client reports any resource changes"
+           })}
+    , {register,
+       sc(ref(translator),
+          #{ desc =>
+"The topic for gateway to publish the register events from LwM2M client.<br>"
+           })}
+    , {update,
+       sc(ref(translator),
+          #{ desc =>
+"The topic for gateway to publish the update events from LwM2M client.<br>"
+           })}
     ];
 
 fields(translator) ->
@@ -180,9 +356,11 @@ fields(tcp_listener) ->
 
 fields(ssl_listener) ->
     fields(tcp_listener) ++
-    [{ssl, sc_meta(hoconsc:ref(emqx_schema, "listener_ssl_opts"),
-                   #{desc => "SSL listener options"})}];
-
+    [{ssl,
+      sc(hoconsc:ref(emqx_schema, "listener_ssl_opts"),
+         #{ desc => "SSL listener options"
+          })}
+    ];
 
 fields(udp_listener) ->
     [
@@ -192,11 +370,10 @@ fields(udp_listener) ->
     common_listener_opts();
 
 fields(dtls_listener) ->
-    [ {acceptors, sc(integer(), 16)}
+    [ {acceptors, sc(integer(), #{default => 16})}
     ] ++
     fields(udp_listener) ++
-    [{dtls, sc_meta(ref(dtls_opts),
-                    #{desc => "DTLS listener options"})}];
+    [{dtls, sc(ref(dtls_opts), #{desc => "DTLS listener options"})}];
 
 fields(udp_opts) ->
     [ {active_n, sc(integer(), 100)}
@@ -215,66 +392,113 @@ fields(dtls_opts) ->
          }, false).
 
 authentication() ->
-    sc_meta(hoconsc:union(
-        [ hoconsc:ref(emqx_authn_mnesia, config)
-        , hoconsc:ref(emqx_authn_mysql, config)
-        , hoconsc:ref(emqx_authn_pgsql, config)
-        , hoconsc:ref(emqx_authn_mongodb, standalone)
-        , hoconsc:ref(emqx_authn_mongodb, 'replica-set')
-        , hoconsc:ref(emqx_authn_mongodb, 'sharded-cluster')
-        , hoconsc:ref(emqx_authn_redis, standalone)
-        , hoconsc:ref(emqx_authn_redis, cluster)
-        , hoconsc:ref(emqx_authn_redis, sentinel)
-        , hoconsc:ref(emqx_authn_http, get)
-        , hoconsc:ref(emqx_authn_http, post)
-        , hoconsc:ref(emqx_authn_jwt, 'hmac-based')
-        , hoconsc:ref(emqx_authn_jwt, 'public-key')
-        , hoconsc:ref(emqx_authn_jwt, 'jwks')
-        , hoconsc:ref(emqx_enhanced_authn_scram_mnesia, config)
-        ]),
-        #{nullable => {true, recursively},
-          desc =>
+    sc(hoconsc:union(
+         [ hoconsc:ref(emqx_authn_mnesia, config)
+         , hoconsc:ref(emqx_authn_mysql, config)
+         , hoconsc:ref(emqx_authn_pgsql, config)
+         , hoconsc:ref(emqx_authn_mongodb, standalone)
+         , hoconsc:ref(emqx_authn_mongodb, 'replica-set')
+         , hoconsc:ref(emqx_authn_mongodb, 'sharded-cluster')
+         , hoconsc:ref(emqx_authn_redis, standalone)
+         , hoconsc:ref(emqx_authn_redis, cluster)
+         , hoconsc:ref(emqx_authn_redis, sentinel)
+         , hoconsc:ref(emqx_authn_http, get)
+         , hoconsc:ref(emqx_authn_http, post)
+         , hoconsc:ref(emqx_authn_jwt, 'hmac-based')
+         , hoconsc:ref(emqx_authn_jwt, 'public-key')
+         , hoconsc:ref(emqx_authn_jwt, 'jwks')
+         , hoconsc:ref(emqx_enhanced_authn_scram_mnesia, config)
+         ]),
+         #{ nullable => {true, recursively}
+          , desc =>
 """Default authentication configs for all of the gateway listeners.<br>
 For per-listener overrides see <code>authentication</code>
-in listener configs"""}).
+in listener configs"""
+          }).
 
 gateway_common_options() ->
-    [ {enable, sc(boolean(), true)}
-    , {enable_stats, sc(boolean(), true)}
-    , {idle_timeout, sc(duration(), <<"30s">>)}
-    , {mountpoint, sc(binary(), <<>>)}
-    , {clientinfo_override, sc(ref(clientinfo_override))}
+    [ {enable,
+       sc(boolean(),
+          #{ default => true
+           , desc => "Whether to enable this gateway"
+           })}
+    , {enable_stats,
+       sc(boolean(),
+          #{ default => true
+           , desc => "Whether to enable client process statistic"
+           })}
+    , {idle_timeout,
+       sc(duration(),
+          #{ default => <<"30s">>
+           , desc =>
+"The idle time of the client connection process.<br>
+it has two purposes:
+1. A newly created client process that does not receive any client requests
+   after that time will be closed directly.
+2. A running client process that does not receive any client requests after
+   this time will go into hibernation to save resources."
+           })}
+    , {mountpoint,
+       sc(binary(),
+          #{ default => <<>>
+           %% TODO: variable support?
+           , desc => ""
+           })}
+    , {clientinfo_override,
+       sc(ref(clientinfo_override),
+          #{ desc => ""
+           })}
     , {authentication,  authentication()}
     ].
 
 common_listener_opts() ->
-    [ {enable, sc(boolean(), true)}
-    , {bind, sc(hoconsc:union([ip_port(), integer()]))}
-    , {max_connections, sc(integer(), 1024)}
-    , {max_conn_rate, sc(integer())}
+    [ {enable,
+       sc(boolean(),
+          #{ default => true
+           })}
+    , {bind,
+       sc(hoconsc:union([ip_port(), integer()]),
+          #{})}
+    , {max_connections,
+       sc(integer(),
+          #{ default => 1024
+           })}
+    , {max_conn_rate,
+       sc(integer(),
+          #{ default => 1000
+           })}
     , {authentication,  authentication()}
-    , {mountpoint, sc(binary(), undefined)}
-    , {access_rules, sc(hoconsc:array(string()), [])}
+    , {mountpoint,
+       sc(binary(),
+          #{ default => undefined
+           })}
+    , {access_rules,
+       sc(hoconsc:array(string()),
+          #{ default => []
+           })}
     ].
 
 tcp_opts() ->
-    [{tcp, sc_meta(ref(emqx_schema, "tcp_opts"), #{})}].
+    [{tcp, sc(ref(emqx_schema, "tcp_opts"), #{})}].
 
 udp_opts() ->
-    [{udp, sc_meta(ref(udp_opts), #{})}].
+    [{udp, sc(ref(udp_opts), #{})}].
 
 proxy_protocol_opts() ->
-    [ {proxy_protocol, sc(boolean(), false)}
-    , {proxy_protocol_timeout, sc(duration(), "15s")}
+    [ {proxy_protocol,
+       sc(boolean(),
+          #{ default => false
+           })}
+    , {proxy_protocol_timeout,
+       sc(duration(),
+          #{ default => "15s"
+           })}
     ].
 
 sc(Type) ->
-    sc_meta(Type, #{}).
+    sc(Type, #{}).
 
-sc(Type, Default) ->
-    sc_meta(Type, #{default => Default}).
-
-sc_meta(Type, Meta) ->
+sc(Type, Meta) ->
     hoconsc:mk(Type, Meta).
 
 map(Name, Type) ->
diff --git a/apps/emqx_gateway/src/mqttsn/emqx_sn_broadcast.erl b/apps/emqx_gateway/src/mqttsn/emqx_sn_broadcast.erl
index dc967681a..0b90d843c 100644
--- a/apps/emqx_gateway/src/mqttsn/emqx_sn_broadcast.erl
+++ b/apps/emqx_gateway/src/mqttsn/emqx_sn_broadcast.erl
@@ -51,6 +51,7 @@ stop() ->
 %%--------------------------------------------------------------------
 
 init([GwId, Port]) ->
+    %% FIXME:
     Duration = application:get_env(emqx_sn, advertise_duration, ?DEFAULT_DURATION),
     {ok, Sock} = gen_udp:open(0, [binary, {broadcast, true}]),
     {ok, ensure_advertise(#state{gwid = GwId, addrs = boradcast_addrs(),
diff --git a/apps/emqx_gateway/src/stomp/emqx_stomp_frame.erl b/apps/emqx_gateway/src/stomp/emqx_stomp_frame.erl
index 1000eec58..d75f77abe 100644
--- a/apps/emqx_gateway/src/stomp/emqx_stomp_frame.erl
+++ b/apps/emqx_gateway/src/stomp/emqx_stomp_frame.erl
@@ -123,7 +123,7 @@ initial_parse_state(Opts) ->
 limit(Opts) ->
     #frame_limit{
        max_header_num = g(max_header_num, Opts, ?MAX_HEADER_NUM),
-       max_header_length = g(max_header_length, Opts, ?MAX_BODY_LENGTH),
+       max_header_length = g(max_header_length, Opts, ?MAX_HEADER_LENGTH),
        max_body_length = g(max_body_length, Opts, ?MAX_BODY_LENGTH)
       }.