# Message monitoring qualifiers

Possible values of D and E in message monitoring topics.

Qualifier | Value | Description
--- | --- | ---
D | `T` | Destination to monitor is a topic. Include the message body in the monitor message as a byte array. Use the `createFromBytes()` method when viewing the monitor message to recreate the message body, if desired.
`t` | Destination to monitor is a topic. Do not include the message body in the monitor message.
`Q` | Destination to monitor is a queue. Include the message body in the monitor message as a byte array. Use the `createFromBytes()` method when viewing the monitor message to recreate the message body, if desired.
`q` | Destination to monitor is a queue. Do not include the message body in the monitor message.
E | `s` | Monitor message is generated when a message is sent by the server to: a consumer a route an external system by way of a transport
`r` | Monitor message is generated when a message is received by the specified destination. This occurs when the message is: Sent by a producer Sent by a route Forwarded from another destination by way of a bridge Imported from transport to an external system
`a` | Monitor message is generated when a message is acknowledged.
`p` | Monitor message is generated when a message prematurely exits due to expiration, being discarded, or a `maxRedelivery` failure.
`*` | Monitor message is generated when a message is sent, received, or acknowledged for the specified destination.

For example, `$sys.monitor.T.r.corp.News` is the topic for monitoring any received messages to the topic named `corp.News`. The message body of any received message is included in monitor messages on this topic. The topic `$sys.monitor.q.*.corp.*` monitors all message events (send, receive, acknowledge) for all queues matching the name `corp.*`. The message body is not included in this topic’s messages.

The messages sent to this type of monitor topic include a description of the event, information about where the message came from (a producer, route, external system, and so on), and optionally the message body, depending upon the value of D. See Monitor Messages, for a complete description of the properties available in monitor messages.

You must explicitly subscribe to a message monitoring topic. That is, subscribing to `$sys.monitor.>` will subscribe to all topics beginning with `$sys.monitor`, but it does not subscribe you to any specific message monitoring topic such as `$sys.monitor.T.*.foo.bar`. However, if another subscriber generates interest in the message monitor topics, this subscriber will also receive those messages.

You can specify wildcards in the destinationName portion of the message monitoring topic to subscribe to the message monitoring topic for all matching destinations. For example, you can subscribe to `$sys.monitor.T.r.>` to monitor all messages received by all topics. For performance reasons, you may want to avoid subscribing to too many message monitoring topics. See Performance Implications of Monitor Topics for more information.

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