Sans is a short skeleton with a dimpled smile and large orbits. He wears an unzipped blue hoodie, a white t-shirt or sweater, black shorts with white stripes, and a pair of sneakers or slippers.He has white pupils that disappear when he is serious. When Sans uses magical psychokinesis, his left eye flashes light blue and yellow, and his right pupil disappears.
Sans is laid back, often sleeping on the job and taking breaks. His laziness is a combination of fatalism and apathy. He wonders if his indolence stems from his knowledge that any progress he makes will be erased when the timeline resets. Conversely, he suggests that this knowledge could be "a poor excuse for being lazy
Though Sans is usually agreeable, he becomes eerily serious at particular moments. He is also observant; Sans reads the protagonist's expressions and can often tell when they have already done certain tasks. He enjoys making bad, skeleton-related puns, although the fact that he performs at the MTT place hints that he may be a talented comedian.He enjoys science fiction and loves to drink ketchup (and possibly other condiments).He also hates making promises.
Sans may have a scientific background. Evidence includes: the quantum physics book,workshop his relationship to alyphs affinity for science,and his timeline research