Check out PlantUML - there's a nice demo here: https://www.planttext.com/ https://www.planttext.com/ Plenty of editors support it, both console (vim/emacs) and

Check out PlantUML - there's a nice demo here: https://www.planttext.com/ https://www.planttext.com/ Plenty of editors support it, both console (vim/emacs) and GUI-based (VSCode, Sublime).