MQTT is lightweight, efficient, and often works well as an interoperability layer between systems. I came to appreciate it more than expected, especially after seeing how many software solutions rely on it in places where I would not have assumed MQTT to be involved.
One thing I kept needing was a simple way to see what was happening on a broker right now.
Which topics are active? What do the messages look like? Are there unexpected topics or payloads? Are multiple message shapes being published under the same topic?
I first came across mqtt-explorer. It is a great tool and already solves most of this problem. The thing I missed most was better diffing. In practice, I often could not easily see what exactly was being sent, especially when completely different message shapes arrived under the same topic.
That is why I built MQTT Radar.
It is a static SPA that connects to a locally running connector. The connector handles the MQTT broker connection, topic subscription, and message collection. The website talks to the connector through local REST endpoints and displays the messages in a way that makes it easier to understand what is happening.
The tool is intentionally small. It does not try to be a full MQTT workbench. It only tries to answer one question:
What is going on on my MQTT broker right now?