This is a small MQTT 3.1.1 client written entirely in GDScript which supports TCP, TLS, WebSocket and secure WebSocket connections and implements retained messages, last wills, subscribing and disconnects.

MQTT is often used to communicate with small remote devices on the network like sensors and switches, also known as Internet of Things (IoT) devices. It works by connecting to a common server on the internet known as a broker and publishing messages to a topic (this looks like a file path separated by slashes "/") and subscribing to the messages of a topic (this uses the wildcards of "*" for a string between two slashes, or "#" for the remainder of the topic).

There are free brokers online you can use such as test.mosquitto.org. This is a simple component that doesn't require much configuration or setup to work and be useful, but for released game you should provision a broker on a server that you own.

Great uses for MQTT in Godot include sharing a high score table between players, controlling lighting effects in the real world, and WebRTC signalling.

To quickly test the simplicity of MQTT, install eclipse mosquitto and try the following two commands in separate windows:

mosquitto_sub -h test.mosquitto.com -v -t "godot/#"

mosquitto_pub -h test.mosquitto.org -t "godot/thing" -m "hi there"