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mqtt-spy vs MQTT.fx: catalog facts
mqtt-spy	MQTT.fx
Free Free and open source under the Eclipse Public License.	Paid Commercial licence with a free trial.
Windows, Command line	macOS
Both a desktop interface and a headless daemon Focused on monitoring MQTT topic activity	Tests broker connections without writing code Eclipse Sparkplug explorer and editor
No packaged releases on the GitHub repository Little recent development activity	Paid after the trial Free open-source MQTT clients cover basic use
Downloadable app	Downloadable app
Open source	Closed source
License: EPL-1.0	License not stated
No account needed	Not stated if an account is needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked October 2, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.