Anything can be keto-friendly if it’s very low in carbs. Egg drop soup from a Chinese restaurant might have thickeners that are high in carbs, so ask about that when you order. (Even if there are some higher-carb ingredients, though, egg drop soup will still be much lower in carbs compared to rice, noodles, and dishes covered in sugary sauces.) If you make it at home, you can control the ingredients to keep it ultra-low-carb.