MQTT over WebSocket Client

Connect directly to your broker, publish and subscribe, and simulate device messages and connection loss.

● Disconnected

01 Connect to Broker

No protocol proxy required

WebSocket URL

Enter the broker WS/WSS URL including its path. Use WSS on HTTPS pages. Native MQTT TCP ports are not supported.

Client ID

MQTT version

Username Optional

Password Optional

Keep Alive (seconds)

Uses a clean session. Subscriptions are cleared on disconnect; subscribe again after reconnecting.

Last Will Optional

Enable Last Will: published by the broker after unexpected connection loss

Will topic

Will QoS

Will format

Will payload Will Retain

Remember settings (excluding password and Will payload)

02 Subscribe to topics

0 subscriptions

+ matches one topic level; # matches remaining levels. The list shows the QoS granted by the broker.

No subscriptions yet.

03 Publish messages

Sent 0 messages

Publish topic

Publish QoS

Payload format

Payload

Retain (keep the last message)Replace payload variables

${timestamp} is Unix time in milliseconds; ${sequence} starts at 1. Variables are not replaced in Hex mode. An empty text or Hex payload with Retain clears the retained message for that topic.

Send intervalseconds

04 Live messages

0 entries

TX 0RX 0Waiting for connection

Connect to a broker, subscribe to a topic, then publish a message. Sent and received messages, QoS and acknowledgments appear here.

Shows the latest 300 entries with up to 4 KB of payload preview each. QoS 0 has no broker acknowledgment. QoS 1/2 acknowledgments appear separately and do not confirm subscriber processing.

Quick test

Connect to your own WS/WSS broker using a unique Client ID.
Subscribe demo/+/telemetry, publish JSON to demo/device/telemetry and inspect the received messages.
Publish with Retain enabled, then subscribe from another client to check the retained message.
Enable Last Will before connecting. Monitor the Will topic from another client, then click Simulate connection loss. A normal disconnect does not trigger the Will.

Supports basic MQTT 3.1.1 and 5.0 connections, publish/subscribe and Last Will. Uses clean sessions without automatic reconnect, persistent sessions or advanced MQTT 5 properties. A subscription to # usually does not match system topics starting with $ .

Your browser sends connections and credentials directly to your broker. Passwords are not saved. Background tabs may throttle timers; connection-loss detection depends on the broker and Keep Alive. For industrial device semantics, use the Sparkplug B Simulator.