MQTT

Rostyman supports MQTT connections for lightweight publish-subscribe messaging.

Creating an MQTT Connection

1. Click the + button in the tab bar → MQTT
2. Or use the New Request dialog and select MQTT

Connection

Broker URL

Enter your MQTT broker URL:

• mqtt://localhost:1883 — standard MQTT
• mqtts://broker.example.com:8883 — MQTT over TLS
• ws://localhost:8083/mqtt — MQTT over WebSocket
• wss://broker.example.com:8084/mqtt — MQTT over secure WebSocket

Connect / Disconnect

• Click Connect to establish a connection
• Status dot: gray (disconnected), yellow (connecting), green (connected), red (error)
• Click Disconnect to close the connection and clear all subscriptions
• Auto-reconnection is enabled (1s interval)

Tabs

Publish

Send messages to a topic:

• Topic — the MQTT topic to publish to (e.g., sensors/temperature)
• QoS — Quality of Service level:
  • QoS 0 — At most once (fire and forget)
  • QoS 1 — At least once (acknowledged delivery)
  • QoS 2 — Exactly once (guaranteed delivery)
• Retain — if checked, the broker stores this as the last known good message for the topic
• Message body — JSON editor for the message payload
• Click Publish to send (only enabled when connected)

Subscribe

Manage topic subscriptions:

• Enter a topic pattern and select QoS level
• Click Subscribe to start receiving messages on that topic
• Active subscriptions are listed below with an × button to unsubscribe
• Supports MQTT wildcards: + (single level), # (multi level)
  • Example: sensors/+/temperature matches sensors/room1/temperature
  • Example: sensors/# matches all topics under sensors/

Settings

Configure connection options (set before connecting):

• Client ID — unique identifier (auto-generated if empty)
• Username — for broker authentication
• Password — for broker authentication
• Keep Alive — ping interval in seconds (default: 60)

Message Log

The bottom panel shows all communication:

• Sent (green ↑) — messages you published (with topic)
• Received (blue ↓) — messages from subscribed topics (with topic)
• System (·) — connection, disconnection, subscription events

Filter buttons: All, Sent, Received, System. Clear button to reset the log.

Each entry shows: timestamp, direction, topic name, and message payload.

Tips

• Subscribe to topics before publishing to see your own messages
• Use # wildcard to monitor all messages on a broker: subscribe to #
• QoS 0 is fastest but messages may be lost; QoS 2 is slowest but guaranteed
• The retain flag is useful for "last will" messages — new subscribers get the latest value immediately
• Most public test brokers: mqtt://test.mosquitto.org, mqtt://broker.hivemq.com