MQTT.fx can be downloaded here

To create a new MQTT client click on the configuration icon next to Connect or from the dropdown Extras → Edit Connection Profiles

Click on the plus icon on the bottom left to create a new MQTT client profile.

Here you have to configure the client to connect with your selected MQTT broker.

The important fields are on the picture below, you can leave the rest on their default settings.

• Profile Name - Write a name for this settings file. A good idea is to name it after the broker you are connecting to.
• Profile Type - Keep as MQTT Broker
• Broker Address - Here enter the IP (or URL) of the broker.
• Broker Port - Here enter the port of the broker. By default it is 1883
• Client ID - This is the name you set for your individual device. There should be only one device with this name connected with your broker.

If you broker has username and password validation enabled then enter them under the “User Credentials” category.

To connect to the broker click on the Connect button as shown in a previous picture. If you are connected successfully the light on the right will turn green otherwise it will turn red and you will get a message Unable to connect to server. After successfully connecting you can publish and subscribe to topics from their respective categories.