MQTTv5 Properties by Message Type

Properties (MQTTv5) are probably one of the most important additions to the MQTT protocol, and are available in most MQTT message types including acknowledgement messages.

The property fields are dependent upon message type, so a CONNECT message will have different property fields than a PUBLISH message.

I have listed the property fields for each message type with links to the online documentation describing the filed and its use.

The user property field is part of the properties field but it’s contents are determined by the user and not defined in the specification. You can find more about it in the Understanding User properties field tutorial.

Connect and Connack
DisConnect
Publish And PUBACK
Subscribe And SUBACK
UnSubscribe And UNSUBACK

Connect and Connack

The Table Below show the property fields available for the Connect and Connection acknowledge messages with links to the online documentation for the field description:

Connect Message

CONNACK Message

3.1.2.11.2 Session Expiry Interval

3.1.2.11.3 Receive Maximum

3.1.2.11.4 Maximum Packet Size

3.1.2.11.5 Topic Alias Maximum

3.1.2.11.6 Request Response Information

3.1.2.11.7 Request Problem Information

3.1.2.11.8 User Property

3.1.2.11.9 Authentication Method

3.1.2.11.10 Authentication Data

3.2.2.3.2 Session Expiry Interval

3.2.2.3.3 Receive Maximum

3.2.2.3.4 Maximum QoS

3.2.2.3.5 Retain Available

3.2.2.3.6 Maximum Packet Size

3.2.2.3.7 Assigned Client Identifier

3.2.2.3.8 Topic Alias Maximum

3.2.2.3.9 Reason String

3.2.2.3.10 User Property

3.2.2.3.11 Wildcard Subscription Available

3.2.2.3.12 Subscription Identifiers Available

3.2.2.3.13 Shared Subscription Available

3.2.2.3.14 Server Keep Alive

3.2.2.3.15 Response Information

3.2.2.3.16 Server Reference

3.2.2.3.17 Authentication Method

3.2.2.3.18 Authentication Data

DisConnect

The Table Below show the property fields available for the Disconnect and Disconnect acknowledge messages with links to the online documentation for the field description:

Disconnect Message

Disconnect Ack Message

3.14.2.2.2 Session Expiry Interval

3.14.2.2.3 Reason String

3.14.2.2.4 User Property

3.14.2.2.5 Server Reference

Publish And PUBACK

The Table Below show the property fields available for the Publish and Publish acknowledge messages with links to the online documentation for the field description:

Publish Message

PUBACK Message

3.3.2.3.2 Payload Format Indicator

3.3.2.3.3 Message Expiry Interval`

3.3.2.3.4 Topic Alias

3.3.2.3.5 Response Topic

3.3.2.3.6 Correlation Data

3.3.2.3.7 User Property

3.3.2.3.8 Subscription Identifier

3.3.2.3.9 Content Type

3.4.2.2.2 Reason String

3.4.2.2.3 User Property

The Table Below show the property fields available for the Subscribe and Subscribe acknowledge messages with links to the online documentation for the field description:

Subscribe Message

SUBACK Message

3.8.2.1.2 Subscription Identifier

3.8.2.1.3 User Property

3.9.2.1.2 Reason String

3.9.2.1.3 User Property

Un-Subscribe And UNSUBACK

The Table Below show the property fields available for the Subscribe and Subscribe acknowledge messages with links to the online documentation for the field description:

Un-Subscribe Message

UNSUBACK Message