I use yafolding minor mode in Emacs, it folds based on indentation level, and it handles indentation-oriented syntaxes like Python and YAML as well as block-oriented syntaxes like C, Java, JS and Ruby.

yaml-mode in Emacs highlights :| text in the quoted string highlight colour, so it's easy to see you're still in the block, or whether you've unindented your way out to the YAML again.

I generally try and split out my yaml such that the quoted blocks don't need to be enormous, though. So, single SQL statements, rather than a whole SQL script, to take one motivating example.

I also use highlight-indentation-current-column mode, for an extra visual aid.