Made from chickpeas and legumes which are later deep-fried in oil, a falafel goes against the basic keto rule against carbs. Falafels may be considered to be low-carb, the carb count as compared to other keto-friendly foods may be too high.
A falafel spikes sugar or glucose levels that reverse the effects of ketosis. That is not the case for all, some falafels can be made from ingredients that can be considered great for a keto diet. Falafels made from cauliflower, hemp hearts, or nuts instead of chickpeas come closer to being a keto-friendly snack as compared to the traditional middle eastern street snack.
One falafel is enough to cater for the carb count serving per day. Therefore, unless you can just stop after just having the one, it is best to keep away from them. Chickpeas contain about 50g of carbohydrates per 10 grams which is a big no in the keto diet world. Stick to recipes with ingredients that are low in carbs and fats but rich in proteins to maintain a keto diet. Consider making a keto falafel using cauliflower, broccoli, some nuts, and seeds. You could add eggs, a few spices, and toasted almond flour just to enhance the flavor.