If you run zigbee2mqtt , Tasmota , ESPHome , Shelly or Frigate through any broker (basic, tls, mtls, websocket), you've probably wondered "is this device actually publishing, and what?" I built fss-mqtt to answer that quickly. It's a keyboard-driven MQTT explorer for the terminal, free and open source. It is built to run forever. You decide how much history you want to track per topic.

fss-mqtt mqtt://homeassistant.local:1883 -u mqtt_user

What it helps with:

Find things fast: type to filter the live topic tree on every keystroke: zigbee2mqtt/, homeassistant/+/+/config, or just part of a device name. Topics flash green as they update, so you can see which devices are talking.

Discovery problems: open any homeassistant/…/config message full screen, with the JSON indented and coloured and the retained flag shown. That makes it easy to spot a wrong state_topic or a stale discovery entry.

Fix retained junk: edit a copy of any message and publish it back (ctrl+e), with any QoS or retain setting.…