Answer: Sweet potatoes are not keto, as they're too high in carbs.
Like most root vegetables, sweet potatoes are highly starchy, which means they're very heavy in carbs. A single 100 g serving of sweet potatoes contains 17 g of net carbs.
As a general rule, vegetables that grow underground are not keto-friendly. For a keto-friendly potato substitute, consider rutabaga or cauliflower.