Working on the level design

Sharing a few pictures from the level design of my game Alpha vs. Zet.

When I'm working on the levels I use the most primitive tools.
The pen and the paper...

I love to work like this somewhere on the coffee.
Looking through the window and take the inspiration...

There will be five types of bosses...
The levels will be more like a simple arena.

I know, I know...
There is still a lot of work to do.
I have only five levels and boss battles are still "work in progress"...

What tools do you use when you are designing the levels?