Looking at https://www.json.org/json-en.html & https://jsonlint.com/ I think the expectation is that the key must be a string and the value must be the json-ised value, so ``` Dictionary new at: 1 put: 2; asJsonString ``` should result in an error.
Consider the first EBNF diagram on https://www.json.org/json-en.html - it can be simplified for this case to { string : jsonised-value}.
Since we're exceptionally clever we could consider doing "make the key be a string of whatever we have" _except_ that trying to reliably convert non-string keys might open up entire pallet-loads of worms. What if somebody is making dictionaries where the keys are complex objects?
Might also want to check on STON as well (https://wiki.squeak.org/squeak/6504). If we're attempting to produce sometihng that meets a standard we should probably actually meet the standard...