description MQTT Overview
MQTT is a lightweight messaging protocol designed for Internet of Things (IoT) applications. It facilitates real-time communication between devices—often referred to as machine-to-machine or M2M—using a publish-subscribe model. Its key features include low latency and decentralized architecture, making it suitable for resource-constrained environments and applications requiring reliable, immediate data exchange. Developers and engineers working with IoT systems benefit from MQTT’s efficiency and security capabilities.
help MQTT FAQ
Is MQTT actually a Bluetooth protocol?
No, MQTT is normally an IP-based messaging protocol that runs over TCP, commonly on port 1883 or 8883 with TLS. Bluetooth devices can feed data into an MQTT system through a gateway, but MQTT itself is not Bluetooth.
Why does MQTT use a broker instead of devices talking directly?
MQTT uses a publish-subscribe model where devices publish messages to topics and a broker such as Mosquitto, HiveMQ, or EMQX forwards them to subscribers. That lets a temperature sensor publish to a topic like home/livingroom/temp without knowing which apps or automations are listening.
What do MQTT QoS 0, 1, and 2 mean in smart home projects?
QoS 0 sends a message once with no delivery guarantee, QoS 1 guarantees at least one delivery, and QoS 2 guarantees exactly one delivery with more protocol overhead. For many Home Assistant sensor updates, QoS 0 or 1 is enough because a new reading arrives shortly after.
What are retained messages and Last Will in MQTT?
A retained message lets the broker keep the latest value on a topic so new subscribers immediately receive the current state. Last Will and Testament lets a client ask the broker to publish a preset offline message if the device disconnects unexpectedly.
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