Answer: Sir Kensington's is keto-friendly, but there are better mayo options.
Mayonnaise is the most popular condiment in America. Sir Kensington's Mayonnaise is keto-friendly at less than 0.5 g of net carbs per tablespoon. It contains 10 g of fat, most of which is unsaturated fat, which helps your body absorb other nutrients.
Sir Kensington's Mayonnaise does list sugar as an ingredient, meaning that the carb count is a little more than zero. Legally, a company can round down to "0 g" if the carbs per serving total less than 0.5 g. While Sir Kensington's is keto-friendly, Primal Kitchen is the better mayo option for those who want to avoid added sugar.
Those who eat vegan keto like Sir Kensington's because it sells a vegan mayo called Fabanaise. Its key ingredient is aquafaba, the water left behind by cooked chickpeas. Its starchy and protein-filled consistency make it the perfect egg-replacement to bind all other ingredients together. Fabanaise does contain 1 g of net carbs per tablespoon, so keep that in mind as you count your macros.