Most hard candy, most gummies and most plain chocolate are gluten free. Four things decide the rest: wheat flour in wafers and cookie pieces, barley malt in chocolate and malted milk, wheat starch dusted on gummies, and licorice, which is bound with wheat flour.
Candy is a good category to learn on, because it is small, the failure modes are few, and they recur everywhere else.
Barley malt. Malted milk, malt balls, and a surprising amount of plain-looking chocolate use barley malt or malt extract for flavor depth. Malt is the reason a chocolate bar with no obvious grain in it can still contain gluten. Barley is not a major US allergen, so the label may name it only as "malt."
Wheat starch as a dusting agent. Gummies and jelly candies are often dusted to prevent sticking, and the dusting agent is sometimes wheat starch. Cornstarch is more common, but the label is the only way to tell.
Licorice. Real licorice candy is bound with wheat flour. It is a flour product with licorice flavoring, and it surprises people more than anything else in the category.
Everything else is usually fine on ingredients: plain hard candy, most caramels, most fruit chews, plain chocolate, marshmallows. Cross-contact on shared lines is the remaining risk, which is why a gluten-free claim still adds something.
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.”
Barley malt is the defining ingredient.
Wheat flour wafer.
Bound with wheat flour. Gluten-free versions exist and say so.
Usually fine; the dusting starch is occasionally wheat.
Usually fine; barley malt appears in some formulations.
Crisped rice cereal is very often malted with barley.
Cocoa, sugar, milk. Check for malt and for wafer inclusions.
Sugar, glucose, flavor, color.
Sugar, gelatin, corn starch.
Traditional licorice candy is not. Wheat flour is the binder that gives it its texture, so it is effectively a flour product. Gluten-free licorice exists and is labeled as such.
Plain chocolate is. The two things to check are barley malt, which is used for flavor depth in some bars and does not have to be named as an allergen, and wafer or cookie inclusions, which are wheat.
Formulations vary by country and get revised, so the right habit is to check the current package rather than memorize a brand list. The ingredients that would disqualify any of them are wheat starch, barley malt and wafer inclusions. Scan the label for those.
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.