Learn MQTT

1883, 8883, 8080, 8081 and 9001, what each broker uses, and how to check a port.

What QoS 0, 1 and 2 guarantee, which packets they send, and which to pick.

How retained messages work, the problems stale ones cause, and how to clear them.

What mosquitto, EMQX, VerneMQ and the rest publish about themselves.

Topics, wildcards, QoS, retained messages, Last Will and sessions.

See every message on the Mosquitto add-on and clear stale discovery configs.

Check what a device publishes, topic by topic, before touching the firmware.