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MQTT Browser

The MQTT Browser is a built-in tool in the BunkerM dashboard that lets you explore your broker's topic tree and message payloads in real time - directly from your browser, without needing any external MQTT client like MQTT Explorer or mosquitto_sub.

What the MQTT Browser Is

The MQTT Browser connects to your BunkerM broker using your BunkerM credentials and provides a graphical interface for:

  • Browsing all topics that have retained messages
  • Viewing the current payload of any retained topic
  • Subscribing to topics to see live message updates
  • Publishing messages to any topic
  • Exploring the topic hierarchy visually

It is especially useful during development, debugging, and when you want a quick look at what your devices are publishing without leaving the BunkerM dashboard.

Connection Note

The MQTT Browser uses your BunkerM session credentials to connect to the broker. It connects as a special internal client with the permissions needed to read topics. You do not need to configure a separate MQTT client or enter credentials manually.

The left panel shows a hierarchical tree of all topics that have retained messages on the broker. Topics are organized by their path segments:

home/
  living-room/
    temperature
    humidity
    light-level
  kitchen/
    temperature
    motion
sensor/
  floor1/
    temp
    humidity

Click any parent node to expand or collapse that branch of the tree. Topics with retained messages show their most recent payload. Topics with recent activity may show a live update indicator.

Viewing a Topic's Payload

Click on any topic name in the tree to view its current retained payload in the detail panel on the right. You will see:

  • Payload - the raw message content, displayed as text or formatted JSON if applicable
  • QoS level - Quality of Service level for the retained message (0, 1, or 2)
  • Retain flag - always true for topics shown in the tree (only retained messages appear in the tree)
  • Timestamp - when the last message was received
  • Size - payload size in bytes

Subscribing to Topics for Live Updates

The topic tree shows retained messages, but many topics carry live messages without the retain flag. To watch a topic in real time:

  1. Click on a topic in the tree (or type a topic pattern in the subscribe box).
  2. Click Subscribe.
  3. New messages on that topic appear in the message panel as they arrive, with timestamps and payloads.

You can subscribe to wildcard patterns to watch multiple topics at once:

  • sensor/# - all topics under sensor/
  • home/+/temperature - temperature topics one level deep under home/

To stop watching a topic, click Unsubscribe next to the subscription entry.

Publishing a Message

You can publish a message to any topic directly from the MQTT Browser:

  1. Click Publish or find the publish panel.
  2. Enter the Topic - the full topic path to publish to.
  3. Enter the Payload - the message content (text, JSON, or any string value).
  4. Select the QoS level (0, 1, or 2).
  5. Check Retain if you want the broker to retain this message for future subscribers.
  6. Click Publish.

The message is published immediately. If you are subscribed to that topic, you will see it appear in the live message feed.

Filtering and Searching Topics

When you have many topics, use the search or filter field at the top of the topic tree to narrow down what you see:

  • Type a partial topic path to filter the tree to matching topics only.
  • Use MQTT wildcard patterns (sensor/#, home/+/temp) to show a subset of topics.
  • Clear the filter to return to the full topic tree.

Understanding Topic Hierarchy

MQTT topics use / as a path separator, similar to a file system. The MQTT Browser displays this as a tree:

  • Parent topics are shown as expandable nodes.
  • Leaf topics are the endpoints that carry actual messages.
  • A topic like home/living-room/temperature has three levels: home, living-room, temperature.

You can publish to any level of the hierarchy. Parent levels (home/, home/living-room/) can also carry their own messages independently of their children.

Viewing Message Metadata

For each message displayed in the MQTT Browser, you can see:

Field Description
Topic Full topic path
Payload Message content
QoS Quality of Service level (0 = at most once, 1 = at least once, 2 = exactly once)
Retain Whether the message is retained on the broker
Timestamp Date and time the message was received by the broker
Size Payload size in bytes

Use Cases

Debugging a device - Your sensor is not behaving as expected. Open the MQTT Browser, find its topic, and check what payload it is actually publishing. Compare against what you expect.

Verifying payloads - After deploying a new firmware version, confirm that the payload format matches what your subscribers expect.

Exploring an existing setup - Taking over an existing MQTT deployment and want to understand what topics are in use? Browse the retained topic tree to get a full picture.

Manual testing - Publish a test command to an actuator topic to verify that the device responds correctly, without needing a separate MQTT client.

Live monitoring - Subscribe to # to watch all traffic in real time during a test or debugging session.

Checking retained state - Quickly check the current known state of all your devices by browsing the retained topic tree.