Sans is a short and big-boned skeleton, wearing a hoodie or simple jacket, unzipped at all times, with a white turtleneck underneath, black shorts and sneakers according to his Steam trading card.

Sans is shown to be very laid-back, sleeping on the job as often as he takes breaks. He enjoys making bad puns relating to skeletons, to the annoyance of his brother. He is kind and reassuring, but becomes eerily serious at abrupt moments (particularly when angry).

He is also very observant. His laziness is noted during the final fight in the genocide route - he is unsure if being somewhat aware of the timeline resetting has broken his spirit, knowing that everything he does will mean nothing... or if he's just using it as an excuse to slack off.

He has obtained the knowledge of multiple timelines and the 'SAVE' function, presumably through his scientific research, as can be found in his room. However, it appears he does not actually retain knowledge when the Frisk loaded a 'SAVE', and cannot use the 'SAVE' function himself.

He likewise is shown to be able to move exceedingly quickly and/or seemingly teleport with his frequent use of "shortcuts" to get places.