Reference/Appendix
v5.14.0

Appendix#

Reference material: file locations, a short glossary, and support links.

File and configuration locations#

MQTT.fx keeps its data in a working directory named MQTT-FX under the OS user data folder:

OSWorking directory
macOS~/Library/Application Support/MQTT-FX/
Windows%USERPROFILE%\AppData\Local\MQTT-FX\
Linux~/MQTT-FX/

It contains:

  • mqttfx-config.xml — connection profiles and application settings
  • mqttfx.log — the log file
  • scripts/ — JavaScript scripts
  • addons/ — payload decoder/editor add-ons

Glossary#

  • QoS (Quality of Service) — delivery guarantee for a message: 0 (at most once), 1 (at least once), 2 (exactly once).
  • Retained message — a message the broker stores for a topic and delivers to new subscribers until it is replaced or cleared.
  • Last Will & Testament (LWT) — a message the broker publishes if a client disconnects unexpectedly.
  • Clean Session (MQTT 3) / Clean Start (MQTT 5) — whether to start without remembered session state.
  • Session Expiry Interval (MQTT 5) — how long the broker keeps a session after disconnect.
  • Wildcards+ matches one topic level, # matches all remaining levels.
  • $SYS — topic hierarchy where a broker publishes its own statistics.
  • Sparkplug B — an MQTT specification for industrial device data, organized into group → edge node (EoN) → device, exchanging typed metrics.
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