Though they are not considered toxic for dogs to eat, it is not recommended that you let your dog eat egg shells.
What Happens if a Dog Eats Egg Shells?
Since egg shells are rich in calcium-carbonate, which is a highly-digestible compound, they can cause a nutritional imbalance for your pup. Your dog should get all of the nutrients he needs from regular dog food, so adding something like egg shells would not be beneficial. Another reason to keep from tossing these your dog’s way is because of the sharp edges that could potentially scratch your dog’s throat.