Very clean and easy to use. I especially love how easy it is to export and import the .json files. So you could actually use them for making dungeon maps.
I especially love that there are even some integrated generators the only thing that would be nice as well is that the dungeon generator also adjusts the canvas size to the size it actually needs. So if you enter 20 as the max size, if it creates a size of 20 it also by itself increases the canvas size to 20.
Additionally the extra features menu comes in the way to actually seeing the canvas so perhaps moving that to the left of the screen could be helpful as well.
Besides that tough the entry is really cool and very well done.