Do note however that this is legal JSON:
[123, 456, 789]
as is
123456
and even
null
In the long past, there were some parsers that would not consider it legal JSON unless it was in an object, but this has been clarified in updates on the standard. I think the (hilariously named) ECMA-404 is the right authority these days though it builds on the IETF RFCs and what is at json.org.