> ## Documentation Index
> Fetch the complete documentation index at: https://docs.coreflux.org/llms.txt
> Use this file to discover all available pages before exploring further.
# Data Viewer
> Subscribe to topics, view the topic tree, and publish messages from the Coreflux HUB
## Why Use the Data Viewer?
You need to see what data is flowing through your broker—which topics are active, what payloads look like, and how to send test messages. The built-in Data Viewer in the Coreflux HUB lets you subscribe to topics, browse the topic tree, and publish messages without installing an external MQTT client.
**An MQTT data viewer built into your Coreflux.** Designed to feel as intuitive as the popular MQTT Explorer desktop app — but with zero installation, right inside the HUB.
## When to Use It
* **Viewing device data** — Subscribe to sensor or device topics to see live readings (temperature, status, etc.) as they arrive
* **Exploring your topic structure** — Browse the Topic Tree to understand which topics exist and how they are organized
* **Verifying Actions** — Subscribe to output topics to confirm your LoT Actions are publishing correctly
* **Debugging** — Inspect payloads and topic structure in real time
* **Testing** — Publish messages to trigger Actions, test Routes, or simulate device data
* **Monitoring broker activity** — Watch `$SYS` topics to check broker health, connected clients, and message throughput
***
## Accessing the Data Viewer
1. In the HUB top navigation, select **MQTT**, then **Data Viewer**.
2. The Topic Tree appears on the left, showing topics as they receive messages.
3. Select a topic to view its payloads in the right panel.
## Topic Tree
The Topic Tree shows the hierarchical structure of topics. Topics appear as messages are received. Expand branches to navigate and select a topic to view its payload history in the payload viewer.
## Exploring Live Data
The Data Viewer is laid out as three vertical panels: **Publish** on the left, the **Topic Tree** in the middle, and a **Detail area** on the right where you build a personal view of the topics you care about right now. You can drag the divider between the tree and the detail area, and collapse the Publish panel into a thin rail to give yourself more room.
**Like an instrument panel for your broker.** Instead of reading rows of raw messages, you pin the topics that matter to the right side and watch them update — values, charts, lamps, even maps — in real time.
### Previewing a topic
Get a feel for what is happening on the broker without committing to a layout. Click any topic in the tree and its latest payload appears in the Detail area as a quick preview.
Each row in the tree carries a small **type icon** that tells you at a glance what kind of value the topic currently holds:
| Icon | Meaning |
| ------------------ | --------------- |
| Glowing orange dot | Boolean `true` |
| Empty dot | Boolean `false` |
| `#` | Number |
| `{}` | JSON object |
| `[]` | JSON array |
| `"` | Plain string |
Rows briefly **flash orange** whenever a new message arrives, so you can see broker activity without staring at every value. To narrow the list, type any part of a topic path into the **Filter** box at the top of the tree — the filter matches anywhere in the path, and the usual display cap is lifted while you are filtering. For broader monitoring, you can also subscribe with a wildcard pattern such as `sensors/#`, and every matching topic appears in the tree as messages come in.
### Tracking what matters
Once a topic is worth watching, **pin it**: double-click the topic, or drag it from the tree onto the Detail area. A card appears for it, and the card shape adapts to the payload so you don't have to mentally decode raw values:
* **Numbers** render as a large value with a **sparkline** of recent history — perfect for sensor readings like temperature or RPM.
* **Booleans** render as a glowing **lamp** — green when `true`, dim when `false`.
* **JSON and text** render with colored keys and an expandable tree, so nested objects stay readable.
* **Geolocation** payloads (latitude/longitude) render as a small **map** with the current point and a trail of recent positions, plus the raw payload underneath.
Cards can be reordered by dragging them up or down, copied to the clipboard with one click, and removed with the **X** in their corner. Add more topics any time from the dashed **+ Add topic** button at the bottom of the cards, which opens a searchable list of every known topic.
### Replaying history with the timeline
As soon as you are tracking topics with more than one message of history, a **timeline** appears at the top of the Detail area. Every tracked topic gets its own color, and every message it has received is drawn as a colored mark on a horizontal track.
From there you can:
* **Click or drag** anywhere on the track to scrub to a moment in time — every card below jumps to the values they had then.
* Step message-by-message with **First / Previous / Next / Last**.
* Hit **Play** to replay the message history like a video, with cards animating through every value.
* Tap **Live** to snap back to the latest message and resume real-time updates (the label turns green when you are caught up).
* Open the gear icon to change the **history buffer** per topic, from 50 up to 2 000 messages — larger buffers give you more scrub range.
While the viewer is focused, the arrow keys step through messages, **Home** jumps to the first, and **End** jumps back to live.
### Drilling into payloads
When a payload is too big to read inline, click its preview in the tree to open the **payload inspector** — a floating window that parses the full payload and lets you expand JSON to any depth. If the payload contains coordinates, the inspector also draws a small map at the top.
For payloads where you only care about one number, drag a single value out of the inspector (or out of a card's expanded JSON tree) onto the Detail area. That value becomes its own **extraction card** — a small card that tracks just that one field, sparkline included if it's numeric. It's the fastest way to follow `temperature` from a 30-field sensor payload without the surrounding noise.
### Drag-and-drop cheatsheet
Most of the viewer is built around dragging. While you are dragging, valid drop zones light up so you can't miss them.
| Drag this | Onto this | Result |
| --------------------------- | -------------------------------- | ------------------------------------------------ |
| A topic in the tree | The Detail area | Adds a tracked card for that topic |
| A topic in the tree | The timeline's topic chips | Adds the topic to the timeline only |
| A topic in the tree | The Publish panel's Topic input | Pre-fills the publish topic |
| A topic in the tree | The Publish panel's Payload area | Pastes the topic's current value |
| A JSON value from a payload | The Detail area | Creates an extraction card for that single field |
| A JSON value from a payload | The Publish panel's Payload area | Pastes just that value |
## Publishing Messages
To publish a test message:
1. Select or enter the target topic.
2. Enter the payload (plain text or JSON).
3. Click **Publish** to send the message.
Use this to trigger Actions, test route configurations, or simulate device data.
***
## Next Steps
See which clients are connected to your broker.
Learn how MQTT topics and wildcards work.