TestMQTT is a browser-based MQTT client: connect to a broker over WebSockets, subscribe to topics with + and # wildcards, publish with QoS 0, 1 or 2 and inspect every payload. It supports MQTT 3.1.1 and MQTT 5, Last Will messages, retained messages and clean sessions.
New to MQTT? Start with how to test an MQTT broker, check the list of public MQTT brokers, or learn which ports your broker uses.
Any MQTT broker that exposes a WebSocket listener, preferably secure WebSockets (wss://). Public brokers are preconfigured; choose “Custom broker” to enter your own URL.
No. Passwords are never saved. The client remembers only non-secret settings such as the selected broker in your browser’s local storage, and connects directly from your browser to the broker.
Public brokers are shared by everyone. TestMQTT creates a random prefix like testmqtt/ab12cd so your test messages do not collide with other users’ traffic.