I think this would be fine, as long as the CSV layer was still parsable using the RFC 4180, then you could still use a normal CSV parser to parse the CSV layer

I think this would be fine, as long as the CSV layer was still parsable using the RFC 4180, then you could still use a normal CSV parser to parse the CSV layer and a normal JSON parser to parse the JSON layer. My worry with your example is that it is neither format, so it will need custom serialisation and deserialisation logic as it is essentially a bran new format. https://datatracker.ietf.org/doc/html/rfc4180 https://datatracker.ietf.org/doc/html/rfc4180 If you’re looking for line-oriented JSON, another option would be ndjson: http://ndjson.org/ http://ndjson.org/