Answer: Black beans are not keto, as they're loaded with carbs.
Black beans are unfortunately very incompatible with the keto way of eating. A half-cup serving of boiled black beans contains 13 g of net carbs, which is high for a side dish. Keep in mind that a half-cup is a relatively conservative serving size, as most restaurants serve beans in quantities closer to a full cup.
If you need a bean to satisfy your bean craving, black soy beans are a popular keto-friendly bean. They're high in protein, rich in antioxidants, and only contain 2 g of net carbs per cup.