Export MQTT messages

Use this action to capture every message published on a topic and write them to a file. A common use is to debug a device or integration, so you can see exactly what it sends over MQTT.

The messages are written to the mqtt_dump.txt file in your configuration folder. Home Assistant listens for the duration you set, then writes the collected messages to the file.

Using this action from the user interface

If you prefer building automations and scripts visually, Home Assistant walks you through this action step by step. You pick what to target, tweak a few options, and save. No YAML knowledge required.

To export messages from an automation or a script:

1. Go to Settings > Automations & scenes.
2. Open an existing automation or script, or select Create automation > Create new automation.
3. If you’re setting up a new automation, add a trigger in the When section. Scripts don’t need a trigger. They run when something else calls them.
4. In the Then do section, select Add action.
5. Search for and select Export.
6. Enter the Topic to listen to. You can use a wildcard, like zigbee2mqtt/#.
7. Optionally, set the Duration to listen for, in seconds.
8. Select Save.

Options in the UI

Using this action in YAML

If you work directly in YAML, or you want to know exactly what Home Assistant does under the hood, this section has the technical reference. It lists the field names you use in YAML, their types, and which ones are required.

In YAML, refer to this action as mqtt.dump. A basic example looks like this:

action: mqtt.dump
data:
  topic: zigbee2mqtt/#

Options in YAML

Good to know

• This action is mainly a debugging tool. You usually run it from Developer tools > Actions when you want to inspect what a device sends.
• The collected messages are written to the mqtt_dump.txt file in your configuration folder. Each run overwrites the previous file.

Still stuck?

The Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with the action you’re calling and what you expected to happen, or share on our subreddit /r/homeassistant.

Related actions

These actions work well alongside this one:

• Publish an MQTT message: Publishes a message to an MQTT topic.

• Reload MQTT entities: Reloads MQTT entities from your YAML configuration.