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Overview

MQTT Explorer provides powerful tools to inspect and analyze MQTT messages in detail. Whether you’re debugging IoT devices, monitoring data flows, or analyzing message patterns, the message inspection features give you complete visibility into your MQTT data.

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Message Details Panel

When you select a topic in the tree, the Details tab displays comprehensive information about the current message: Message Metadata
  • Topic path with breadcrumb navigation
  • Message payload (current value)
  • Timestamp of when the message was received
  • Message ID (if available)
  • QoS (Quality of Service) level
  • Retained message indicator
  • Payload size in bytes
The breadcrumb navigation at the top shows the full topic hierarchy and allows you to click through to parent topics.

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Payload Rendering

MQTT Explorer intelligently formats message payloads based on content type:

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Automatic Format Detection

JSON

Automatically detects and formats JSON with syntax highlighting and indentation

Plain Text

Displays readable text with proper line breaks and whitespace

SparkplugB

Decodes SparkplugB protocol messages with proper structure

Base64 Binary

Shows binary data in readable base64 encoding

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Syntax Highlighting

The code editor provides:
  • Color-coded JSON: Keys, values, strings, numbers, booleans
  • Line numbers: Easy reference for large payloads
  • Collapsible sections: Fold/unfold JSON objects and arrays
  • Theme aware: Automatically adjusts to light/dark mode
For JSON payloads, you can click on object/array indicators to collapse or expand sections for easier navigation.

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Message History

Every topic maintains a complete history of messages: History Features
  • Unlimited history: Stores all messages received during the session
  • Chronological order: Most recent message first
  • Quick navigation: Click any historical message to view it
  • Timestamp display: See exactly when each message arrived
  • Payload preview: Truncated preview in the history list
1

Open History

Click the clock icon or “History” button in the Details tab
2

Browse Messages

Scroll through the list of historical messages
3

Select Message

Click any message to view its full payload and metadata

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Diff Comparison Mode

Compare messages to track changes over time:

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Side-by-Side Comparison

The diff viewer shows:
  • Side-by-side layout: Current and previous messages side by side
  • Change highlighting: Added, removed, and modified lines
  • Line numbers: Corresponding line numbers for both versions
  • JSON-aware diffing: Intelligent comparison of JSON structures

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Comparison Options

Automatically compares the current message with the immediately previous message in the history. This is useful for tracking incremental changes.
Choose any message from the history to compare with the current message. Perfect for comparing states across a longer time period.
Toggle between:
  • Diff Mode: Shows differences between two messages
  • Raw Mode: Shows both messages in full without highlighting differences
Diff comparison is most effective with JSON payloads, where structural changes are clearly highlighted.

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Copy & Save Actions

Extract message data for external use:

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Copy Features

  • Copy payload: Copy the raw message payload to clipboard
  • Copy topic path: Copy the full topic string
  • Copy timestamp: Copy the message timestamp
  • Copy as JSON: Export message metadata and payload as JSON

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Save to File

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Click Save Button

Click the save icon in the value renderer
2

Choose Format

Select format (raw payload, JSON, or formatted)
3

Select Location

Choose where to save the file on your system
Use the save feature to capture message snapshots for documentation, bug reports, or data analysis.

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Value Rendering Display Modes

Customize how messages are displayed:

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Display Mode Options

Diff Mode (Default)
  • Highlights changes between current and previous messages
  • Shows added/removed content in different colors
  • Best for tracking state changes
Raw Mode
  • Shows complete message payload without comparison
  • Displays both current and selected messages separately
  • Ideal for reviewing full message content
Chart Mode (for numeric values)

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Format Detection & Decoding

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Automatic Decoding

MQTT Explorer automatically detects and decodes: JSON Payloads
  • Validates JSON syntax
  • Pretty-prints with proper indentation
  • Shows parsing errors if invalid
SparkplugB Protocol
  • Decodes SparkplugB metric messages
  • Displays metrics in readable format
  • Shows metric names, values, and types
  • Indicates decoding with “Decoded SparkplugB” label
Binary Data
  • Displays as base64-encoded string
  • Shows byte count
  • Indicates non-text content
SparkplugB is an MQTT topic and payload specification for Industrial IoT. MQTT Explorer can automatically decode SparkplugB messages to show the embedded metrics and metadata in a readable format.

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Topic Type Indicators

Understand what kind of data each topic contains:
  • JSON Object: {...} icon
  • JSON Array: [...] icon
  • String: "abc" icon
  • Number: 123 icon
  • Boolean: true/false indicator
  • Binary: Binary data indicator
The topic type is automatically detected from the message payload and displayed in the topic panel.

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Delete Messages

Remove topics from your local tree view: Delete Options
  • Single Topic: Delete just the selected topic
  • Recursive Delete: Delete topic and all its children
  • Confirmation Dialog: Prevents accidental deletion
Deleting a topic only removes it from your local view. It does not delete the message from the broker or unsubscribe from the topic.

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Best Practices

Use History for Debugging

Review message history to identify when values changed or errors occurred

Compare States

Use diff mode to track configuration changes or state transitions

Export Important Messages

Save critical messages for documentation or troubleshooting

Monitor Payload Sizes

Check message sizes to optimize bandwidth and storage