PlantUML is free and open source and will always be.

However hosting the service and enhancing the product takes time and money.

So PlantUML can occasionally display sponsored or advertising messages. Those messages are usually generated on welcome or error images and never on fonctional diagrams.

Here is an example of such display:

If this is unacceptable for you and if you are using PlantUML in a professional environment, there is a way for you to disable these sponsored or advertising messages.

You may indeed ask for a license key by running the following special diagram:

You then have to send us the result (which is a footprint of your server or machine). We will send you back a software key that you will install on your machine (by running another simple and special command).

Once the software key is installed, we will be switched into the Professional Edition that do not print any sponsored or advertising messages. You will be able to double check this by running:

Thanks for your support!