I think it is good to require quotation marks for strings, at least for values (although I could live with it if quotation marks for strings are allowed even if not required, since then, if you do not like the feature of not having quotation marks for strings, you can just not use that feature).
Maybe it would be sense if quotation marks were not required for keys with only a restricted character set which are not an empty string, though.
No quotes around keys would be sufficient, honestly. I use YAML a lot for API documentation, and there are still some cases where wrapping your values in quotes is necessary. But requiring it for keys becomes very annoying.
Maybe it would be sense if quotation marks were not required for keys with only a restricted character set which are not an empty string, though.