A fictional pottery shop receives {"quantity":12,"quantity":120}. Its AI assistant says the format check passed and the order can ship. But does the customer want twelve mugs or one hundred twenty? This is not a contest to pick the more plausible answer. One object contains the quantity name twice. Keep the order in review before either interpretation reaches fulfillment.

RFC 8259 recommends unique names within a JSON object. It describes differing receiver behavior for duplicates: keeping the last pair, reporting an error, or preserving all pairs.[1] Python documents a concrete case: its default decoder retains the final value.[2] Successful parsing therefore describes one parser’s behavior, not a settled business meaning.

In an isolated environment, we passed that synthetic text to Python’s default decoder and obtained quantity 120. An object_pairs_hook that checks for repeated names rejected it instead. No shop or shipping system was connected, and this does not establish every language’s behavior. The important observation: once the first parse discards a value, a later check of that dictionary cannot see the original conflict.

We recommend detecting repeated names per object while parsing the original JSON at intake, before field, range and business-approval checks. Use a complete parser rather than a regular expression; cover nested objects too. The same name in two separate objects is not this kind of duplicate. For rejected data, retain a controlled source reference and error location, assign a correction owner, and avoid copying complete customer records into logs.

Our acceptance checklist asks whether a normal single field passes, a repeated quantity in one object is rejected, a nested duplicate is rejected, and two separate objects with their own quantity remain valid. Also verify that rejection causes no warehouse action and that a person can locate the order needing correction. Beyond the local parsing experiment above, these workflow checks are recommendations, not customer-system tests. AI can explain the ambiguity; it cannot guess the customer’s order.