Private broker Open client
Free · No sign-up · Runs in your browser

Test MQTT brokers online in seconds

TestMQTT is a free web-based MQTT client. Connect to any broker over WebSockets, subscribe to topics, publish messages and debug your IoT data flow — without installing anything.

Open MQTT client Browse public brokers
  • MQTT 3.1.1 & 5
  • QoS 0 / 1 / 2
  • Retained & Last Will
  • JSON inspector

MQTT broker speed test

Connect + publish/subscribe round trip, measured from your browser.

  • ConnectMQ Recommendedwss://broker.connectmq.com:8084/mqtt
    —Open
  • HiveMQ Public Brokerwss://broker.hivemq.com:8884/mqtt
    —Open
  • EMQX Public Brokerwss://broker.emqx.io:8084/mqtt
    —Open
  • Eclipse Mosquitto Test Serverwss://test.mosquitto.org:8081
    —Open
  • Eclipse Projects Brokerwss://mqtt.eclipseprojects.io:443/mqtt
    —Open
Public brokers are shared and best-effort — results vary with load.Need a dedicated broker? →
Everything you need to debug MQTT

A complete MQTT test client in a browser tab

From a first connection check to inspecting JSON telemetry, TestMQTT covers the workflow you would otherwise need a desktop tool for.

Connect to any broker

Pick a public broker or paste your own wss:// URL. Username, password, client ID, keep-alive, MQTT 5 and Last Will supported.

Publish & subscribe

Subscribe with + and # wildcards, publish with QoS 0/1/2 and the retain flag, and watch messages stream in real time.

Live topic tree

Every topic you receive is organised into a browsable tree with message counts, so you can understand a broker at a glance.

JSON-aware inspector

Payloads are detected as JSON, numbers, text or binary and pretty-printed. Numeric topics get an instant sparkline.

Clear retained messages

Remove stale retained messages with one click — the client publishes the empty retained payload for you.

Shareable test links

Deep-link a broker and topic (/client?broker=emqx&topic=…) to reproduce a test with a teammate.

How to test MQTT in three steps

  1. Connect

    Choose a broker and press Connect. A green status means the broker accepted your client.

  2. Subscribe

    Subscribe to your own topic prefix — TestMQTT suggests a unique one so you only see your data.

  3. Publish & verify

    Send a message and watch it arrive. Inspect payload, QoS, retain flag and timing.

Read the full guide to testing an MQTT broker →

Public MQTT brokers you can test right now

Connection details for the most popular free MQTT brokers, each one ready to open in the client.

ConnectMQ

broker.connectmq.com
Recommended

Managed MQTT broker with private, authenticated instances — built for teams moving from testing to production.

Test now Ports & details
From the makers of TestMQTT

Outgrown the public sandbox?

Public test brokers are shared with thousands of strangers. ConnectMQ gives you a private MQTT broker you can trust with real devices — set up in minutes.

Create your broker Learn about ConnectMQ
  • Your own isolated broker — nobody else can read your topics
  • Username / password auth and per-topic access control
  • TLS and secure WebSockets, MQTT 3.1.1 and MQTT 5
  • Same client code from first test to production

Learn MQTT

Practical guides for developers working with MQTT and IoT messaging.

Guides

How to Test an MQTT Broker (Online, CLI and Code)

Learn how to test an MQTT broker: check connectivity, publish and subscribe, verify QoS and retained messages, and debug failures — online, with the CLI or in code.

7 min readFundamentals

What Is MQTT? A Practical Introduction

What is MQTT? A practical introduction to the MQTT protocol: brokers, topics, publish/subscribe, QoS, retained messages and Last Will — with hands-on examples.

7 min readFundamentals

MQTT Ports Explained: 1883, 8883, 8083, 8084 and 443

Which MQTT port should you use? Learn what ports 1883, 8883, 8083, 8084 and 443 mean, which work in a browser, and the exact ports of popular public brokers.

6 min readGuides

Public MQTT Brokers vs Private Brokers: When to Switch

Public MQTT brokers are great for testing but risky for real data. Learn their limits, when they are fine, and what to look for in a private MQTT broker.

7 min readGuides

Best MQTT Brokers Compared: Mosquitto vs EMQX vs HiveMQ vs Managed

An honest MQTT broker comparison: Mosquitto, EMQX, HiveMQ, VerneMQ, NanoMQ and managed cloud brokers — language, clustering, MQTT 5, licenses and how to choose.

8 min readTutorials

How to Install Mosquitto MQTT Broker (Ubuntu, Debian, Windows, macOS)

Install the Mosquitto MQTT broker on Ubuntu, Debian, Windows or macOS, run it as a service, test it with mosquitto_sub/pub and fix the 2.x local-only mode.

7 min read

All MQTT guides →

Free MQTT tools

Generators and calculators for the parts of MQTT work that don't need a live broker.

MQTT Code Generator

Generate ready-to-run MQTT client code for Python, JavaScript, Node.js, ESP32/Arduino, Go and the Mosquitto CLI.

mosquitto.conf Generator

Build a Mosquitto broker config with listeners, WebSockets, TLS, password authentication and persistence.

MQTT Reason Code Lookup

Look up any MQTT 3.1.1 return code or MQTT 5 reason code — what it means and how to fix it.

Topic Wildcard Tester

Check which topics a subscription filter matches, including + and # wildcards and $SYS rules.

Packet Size & Bandwidth Calculator

Calculate the exact MQTT PUBLISH packet size and the monthly data usage of your device fleet.

Client ID Generator

Generate unique, spec-compliant MQTT client IDs in bulk with your own prefix and format.

Frequently asked questions

How do I test an MQTT broker online?

Open the TestMQTT client, choose a broker or enter its secure WebSocket URL, click Connect, subscribe to a topic and publish a message to the same topic. If the message comes back, the broker works.

Is TestMQTT free?

Yes. TestMQTT is free, needs no account and runs entirely in your browser. Connection settings never leave your machine except to reach the broker you choose.

Why does TestMQTT only use WebSockets?

Browsers cannot open raw TCP connections, so any web-based MQTT client has to use the broker’s WebSocket listener (ws:// or wss://). Most brokers expose one, often on ports 8083/8084, 8000/8884 or 443.

Can I connect to a broker on localhost?

Yes, if your broker has a WebSocket listener. Because this site is served over HTTPS, browsers usually require wss://. For local brokers, enable TLS on the WebSocket listener or use a tunnel.

Are public MQTT brokers safe to use?

They are fine for experiments, but everything you publish is visible to anyone. Use unique topic names and never send credentials or personal data. For real devices use a private broker with authentication.