The gluten grains, every alias they travel under, and the one grain whose answer changes depending on which country you are in.
Wheat, barley and rye are gluten grains everywhere. Oats are the contested case: the FDA does not classify them as a gluten grain, Canada does, and Australia and New Zealand ban them from gluten-free food entirely, certified or not.
Point CiCi at the barcode on anything on this list and get this same reasoning in about two seconds, plus the carbs and whether it has been recalled. 360,000+ packaged foods are already read and waiting.
Each guide covers a whole aisle and explains the mechanism, which is more portable than any list of names.
This site answers the question you knew to ask. The app answers the one you didn't: the barley malt in a rice cereal, the wheat starch in a gummy. Scan the barcode, or photograph the panel when the barcode isn't in any database, and CiCi shows which words on the label produced the answer.
14 days free, then $29.99 a year. Cheaper than Fig, and it does what three separate apps do. This website stays free forever either way: every answer on it, permanently, with no account.