The following public brokers are useful:
Mosquitto MQTT Testbroker
Host: test.mosquitto.org
TCP Port: 1883
TLS Port: 8883
TLS with Client Certificate Port: 8884
HiveMQ MQTT Testbroker
Host: broker.hivemq.com
TCP Port: 1883
These broker channels are entirely open, so beware what data you share.
Read Caveats for a good understanding of their service availability
https://test.mosquitto.org/ for more info
http://broker.hivemq.com/ for more info
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