MQTT Tester
MQTT Tester
Connect to an MQTT broker over WebSockets, subscribe to topics, publish messages, and inspect a live message log — all from your browser.
No active subscriptions.
No messages yet. Connect, subscribe to a topic, and publish a message to see it here.
Connects to an MQTT broker using MQTT-over-WebSockets (via MQTT.js). Nothing is sent anywhere except to the broker you specify — this tool does not proxy or log your traffic. Payloads that aren't valid UTF-8 text are shown as hex.
MQTT Tester
Connect to an MQTT broker over WebSockets, subscribe to topics, publish messages, and inspect a live message log — all from your browser.
Common uses
- Subscribe to a topic and watch live sensor messages
- Publish a retained message to an MQTT broker
- Test an IoT device topic hierarchy
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Frequently asked questions
Can I connect to an MQTT broker from the browser?
Yes, if the broker exposes a WebSocket listener (ws:// or wss://). This MQTT tester connects over WebSockets, so it cannot reach a plain TCP broker on port 1883.
How do I subscribe to a topic and see live messages?
Connect to your broker URL, add a topic filter (wildcards such as + and # are accepted by the broker), choose a QoS and subscribe. Incoming messages appear in the live message log.
How do I publish a retained MQTT message?
Enter the topic and payload in the publish panel, tick Retain, choose a QoS level, then publish. The broker stores the message for new subscribers.
Can I set a Last Will and Testament?
Yes. Tick the Last Will & Testament option before connecting and give it a topic, payload, QoS and retain flag; the broker publishes it if the client disconnects ungracefully.
Why does my MQTT connection fail in the browser?
The most common causes are connecting to a TCP port instead of a WebSocket port, using ws:// from an https page (use wss://), or a broker that requires credentials. Check the URL, path and username/password.
Is my data uploaded to a server?
No. This tool runs entirely in your browser — your input is processed locally on your device and is never uploaded or stored on a server.