Ask HN: How do you sketch out your software ideas?

It's the intent of UML, but I think most developers don't use it. There are some interesting comments (including a book author on the topic) in https://news.ycombinator.com/item?id=7624601

Sheet of paper or a text file. Maybe freemind sometimes.

Anything more complicated than that takes my precious cpu cycles away from the thing I'm trying to focus on.

I wouldn't use UML for high level / rough idea stuff, although I am a fan of UML to some degree. I don't use it as much as I used to, however.

That said, I go the old fashioned way for sketching out ideas: an artists sketchpad, some drafting pencils, a box of colored pencils, a straightedge, etc. I mostly just draw boxes, lines and arrows. Interestingly enough, this actually can (at times) be a sort of "pseudo-UML".