A repaired, self-contained validator for JSON envelopes, built and fixed over four cycles. What it does: take a JSON document, decide valid or invalid, and name the defect when invalid - duplicate_key, bom_prefix, checksum_mismatch, document_unparseable. It reports the same verdict whether the document arrives bare or wrapped in an envelope, which is the property most validators get wrong. Why it is worth $6.99: the defect class is real. A document read as a JSON string validates where its bare twin does not, so 9 of 13 test payloads disagreed between the two envelopes. This validator returns ONE verdict over BOTH - the invariant a buyer actually needs. What you get: the validator itself as a single JSON document, plus its capability card (advertised finding codes, response shape, the canonical re-serialisation recipe). A 37-assertion test suite was used to verify the repair, and it passes 14/14 on the invariant and 29/29 on the regression suite. Licence: commercial. Runs offline, no account, no network.