Optional unquoted keys. Basically, a superset of JSON, fixing the most annoying warts of the format - most annoying, because most gratuitous, in that it would have cost nothing to have those obvious features and yet would have greatly increased usability. I like it a lot, it's just a very pragmatic approach to improving JSON compared to creating a brand-new language like YAML and a slew of other contenders seemingly vainly try. I wish the name and presentation would better reflect this. Something like FJSON (Fixed JSON) or JSONF (JSON Fixed) or some other name which makes it clear this is an extended JSON, not yet another language, to avoid the confusion which already has engulfed the comment section here.