A cereal made from rice or corn is still usually not gluten free, because barley malt is the standard flavouring in the category. This is the most common surprise on a supermarket shelf.
Cereal is the clearest demonstration of why an ingredient-list scanner that only looks for the word "wheat" is dangerous.

This matters more than it first appears, because barley is not a major food allergen under US law. Wheat inside an ingredient must be declared; barley need not be identified as barley. On a cereal box it usually appears as "malt flavoring" or "malt extract," and a person scanning for "wheat" sails straight past it.
Manufacturers have responded by producing separately formulated gluten-free versions of several well-known cereals, using a different flavouring. These are different products in different packaging, not a relabelling. Look for the gluten-free claim on the box rather than the grain on the front.
Granola adds a second issue on top: oats, with all the supply-chain questions that carry, plus barley malt syrup as a common sweetener.
Point CiCi at the barcode 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.
Sorted by what the answer actually is, rather than alphabetically — because the useful question in a shop is “which pile is this in.”
Corn, flavoured with barley malt.
Rice, flavoured with barley malt.
Wheat.
Oats plus, very often, barley malt syrup.
Only when the oats are certified gluten free. See the oats guide.
Separately formulated with a different flavouring. Check the box, not the brand.
Single ingredient, no malt.
Corn. Watch shared milling for the finer grinds.
Buckwheat is unrelated to wheat.
Because they are flavoured with barley malt. The grain is corn, but malt extract from barley is the traditional flavouring, and it puts the product above the 20 ppm threshold. Separately formulated gluten-free versions exist.
The classic US formulation contains malt flavouring from barley and is not. There is a separately formulated gluten-free version made with brown rice. The gluten-free claim on the box is what tells them apart.
Only when it says so. Granola is oat-based, which raises the oat supply-chain question, and barley malt syrup is a common sweetener in the category.
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.