MQTT $SYS Topics: What Broker System Topics Tell You
A practical guide to the $SYS topic tree: where it comes from, why wildcards skip it, what Mosquitto-style brokers publish there and how to watch client connection state on ConnectMQ.
8 min read
Blog
MQTT Fundamentals
Core MQTT concepts explained: brokers, topics, QoS, sessions and MQTT 5 features, with hands-on examples on the free public broker broker.connectmq.com.
MQTT Fundamentals
MQTT vs DDS: Brokered vs Brokerless Industrial Messaging
MQTT routes through a broker; DDS lets peers discover each other and exchange typed data directly. This comparison covers architecture, real-time guarantees, robotics versus IIoT use and how to bridge the two.
7 min read
How Does MQTT Work? Brokers, Clients and Messages Explained
A step-by-step explanation of how MQTT works, from opening a TCP connection to CONNECT, SUBSCRIBE, PUBLISH, keep alive and disconnect, with a trace you can reproduce on a public broker.
7 min read
MQTT Wildcards: How to Use + and # in Topic Filters
The single-level + and multi-level # wildcards let one MQTT subscription cover many topics. Learn the exact matching rules, the edge cases and how to test every filter on a live broker.
7 min read
MQTT Ports Explained: 1883, 8883, 8083 and 8084
A practical guide to MQTT ports: plain TCP 1883, TLS 8883, WebSocket 8083 and secure WebSocket 8084, with firewall advice and copy-paste tests against broker.connectmq.com.
7 min read
MQTT Keep Alive Interval: How to Choose the Right Value
The keep alive interval decides how fast a broker notices a dead connection and how much traffic and battery an idle client burns. Here is how it works and how to pick a value.
9 min read
MQTT Packet Structure: Fixed Header, Variable Header and Payload
A byte-level walkthrough of MQTT packets: how the fixed header encodes type and flags, how remaining length works, and what the variable header and payload contain, using a CONNECT and PUBLISH you can capture with Wireshark.
7 min read
MQTT Client ID Best Practices: Uniqueness, Format and Takeovers
The client ID is how an MQTT broker knows who you are. Get it wrong and devices kick each other offline or lose their sessions. Here are the rules, formats and debugging steps that work.
7 min read
MQTT 5 User Properties: Adding Metadata Without Touching the Payload
MQTT 5 user properties are key/value headers you can attach to a message without changing its payload. Learn how they work, what they are good for, and how to send and read them in Python, Node.js and the CLI.
7 min read
MQTT Testing Checklist: 12 Checks to Run Before Go-Live
A go-live MQTT testing checklist with quick, repeatable tests for reconnects, QoS, retained messages, Last Will, payload validation, limits and load, all runnable against a free public broker.
9 min read
MQTT Shared Subscriptions: Load Balancing Message Consumers
Shared subscriptions turn MQTT into a work queue: each message goes to one member of a consumer group. Learn the $share syntax, delivery semantics, scaling patterns and how to test support.
7 min read
MQTT Receive Maximum: Flow Control for Slow Devices in MQTT 5
Receive Maximum is MQTT 5's built-in flow control. It caps how many unacknowledged QoS 1 and 2 messages can be in flight, so slow devices are not overwhelmed after a reconnect.
7 min read
All 15 MQTT Control Packet Types Explained
MQTT has just 15 control packet types. This reference explains each one, from CONNECT to AUTH, with its type number, direction, first byte and what it looks like in debug logs while you troubleshoot.
7 min read
MQTT vs HTTP for IoT: Which Protocol Should You Use?
A practical MQTT vs HTTP comparison for IoT covering message overhead, push versus polling, battery life and connection models, with a small benchmark you can run yourself.
8 min read
MQTT vs Kafka: Device Messaging vs Event Streaming
MQTT and Kafka are not competitors so much as neighbors. This guide explains what each one is built for, compares them side by side and shows how to feed Kafka from an MQTT broker with an external consumer service.
8 min read
MQTT vs AMQP: Differences, Use Cases and Performance
MQTT and AMQP are both brokered messaging protocols, but they solve different problems. This comparison covers routing, delivery guarantees, footprint and typical architectures so you can pick with confidence.
8 min read
What Is an MQTT Broker? A Beginner's Guide to Publish/Subscribe Messaging
An MQTT broker is the hub that routes every message between IoT devices and apps. Learn publish/subscribe, topics and wildcards, sessions, QoS, retained messages and last will, then try it hands-on in minutes.
9 min read
MQTT Session Expiry Interval and Clean Start in MQTT 5 Explained
MQTT 5 split the old clean session flag into Clean Start and Session Expiry Interval. Here is how the two combine, which values to choose and how to verify them on a live broker.
7 min read
MQTT Topic Hierarchy Examples for Real IoT Projects
Ready-to-copy MQTT topic trees for smart home, fleet tracking, factory and energy monitoring projects, each with the wildcard subscriptions it is designed for and the mistakes to avoid.
7 min read
MQTT Device Online/Offline Status with LWT and Retained Messages
A step-by-step presence pattern for MQTT fleets: retained birth messages, a retained Last Will, graceful shutdown messages and a monitor that tracks every device's state in real time.
7 min read
MQTT vs NATS: Choosing a Messaging System for IoT
MQTT and NATS are both lightweight publish/subscribe systems, but they target different clients. This comparison covers device support, delivery guarantees, persistence and ecosystem so you can place each one correctly.
7 min read
MQTT QoS Levels Explained: QoS 0, 1 and 2 with Packet Flows and Examples
A practical guide to MQTT QoS: how QoS 0, 1 and 2 work on the wire, why the delivered QoS can be lower than you asked for, how sessions queue messages and which level to choose for each use case.
9 min read
MQTT Tutorial: The Complete Beginner's Guide to MQTT
A hands-on MQTT tutorial for beginners: learn brokers, topics, QoS, retained messages and Last Will, then publish and subscribe for real on the free broker.connectmq.com with the CLI, Python and JavaScript.
12 min read
MQTT Persistent Session and the Clean Session Flag Explained
A persistent session lets a broker remember a client's subscriptions and queue its QoS 1 and 2 messages while it is offline. Learn what is stored, when to use it and the pitfalls to avoid.
7 min read
The MQTT Publish Subscribe Model: Decoupling Devices and Apps
The MQTT publish subscribe model lets devices and apps exchange data without knowing about each other. Learn the three kinds of decoupling and try them live with two clients on broker.connectmq.com.
8 min read
MQTT vs WebSocket: Protocol or Transport?
WebSocket and MQTT are often compared, but one is a transport and the other a messaging protocol. Learn what raw WebSocket apps must build themselves and how to run MQTT over secure WebSocket in the browser.
7 min read
MQTT Topic Alias: Saving Bandwidth on Long Topic Names
MQTT 5 topic aliases replace long topic names with a two-byte number after the first publish. Learn how the negotiation works, how many bytes you actually save and how to use aliases safely from MQTT.js.
7 min read
Handling Duplicate MQTT Messages with QoS 1
QoS 1 means at least once, and sometimes that means twice. Learn why MQTT duplicate messages happen, why the DUP flag alone cannot save you, and how to build idempotent consumers that handle them safely.
7 min read
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