I don't use any tools for that. I did try an online ascii-drawing tool one afternoon, but the results weren't compact enough to be useful for programming commen

I don't use any tools for that. I did try an online ascii-drawing tool one afternoon, but the results weren't compact enough to be useful for programming comments. Contrary to the way I worded my comment, my 'diagrams' are typically no more than text with perhaps a box-drawing unicode character here or there. But even drawing a simple tree, tabs can mess up important details.