> An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a string, number, boolean, null, object, or array.

https://tools.ietf.org/html/rfc7159#section-1

As of Python 3.6 (in theory not guaranteed until Python 3.7), key order is preserved when reading and writing. That's a consequence of the fact Python dictionaries can now remember the order of insertion.

It's true that it doesn't support duplicate keys though (unless you pass in a different class to the object_pairs_hook parameter of loads() to replace its use of dict).