TL;DR

If you’re in a hurry, PlantUML has an online server.

One interesting feature of PlantUML over sdedit is that you don’t need to install anything if you’re really in a hurry (or you don’t want to install anything).

The online server allows you to design your graphs online. The fun thing is that its API encodes the full diagram into the URL, so as long as the online server is… online, you should see an example picture here:

I guess that in 2021 we’re a little spoiled and not used to hit the submit button to see the updates in our editing… but hey! It’s free and immensely useful even without the cool things of today’s web!