SANS SIMULATORRead the pattern
Watch where the bones appear. Small, deliberate movements leave room for the next attack.
Sans Simulator
A familiar face. A very bad time.
Illustrative artwork · Game by Jcw87
Keep your cool
Red soul? Move freely. Blue soul? Gravity takes over. Hold the jump to go higher.
Try again
A missed dodge is a pattern learned. Practice one attack before taking on the whole fight.
Find your fight.
Select a mode from the in-game menu.
Normal
Take on the full sequence. Every dodge counts.
Practice
Learn the fight with more room to make mistakes.
Endless
Keep dodging and see how long you can last.
Single attack
Work on the pattern that keeps catching you.
Already know the patterns? Explore Custom Attack in the game menu.
A few things to know.
FAQWhat is Sans Simulator?
It’s a fan-made recreation of the Sans boss fight from UNDERTALE. This site runs Jcw87’s Bad Time Simulator: you control the heart, dodge attacks, and use the battle menu between turns. You play against Sans.
Do I need to have played UNDERTALE?
No. You can learn the controls here and start with Practice. The fight references a late-game UNDERTALE encounter, so expect spoilers if you plan to play the original story.
What are the controls?
Use the arrow keys to move. Z or Enter confirms a selection; X or Shift cancels. Hold X or Shift to slow your movement in battle. On touch devices, use the game’s directional pad and action buttons.
What is the difference between a blue soul and blue bones?
A blue soul changes movement: gravity pulls you down and you must jump. Blue bones are an attack type: stay still as they pass. White bones hurt on contact. Watch the soul and the attack separately.
Can I play on my phone?
The game includes touch controls. Rotate your phone to landscape for a larger arena, or open the game directly if fullscreen is unavailable. A keyboard gives more precise movement for difficult patterns.
Open game in a new tab ↗The game isn’t loading. What should I do?
Press Restart to reload the game, or refresh this page. Make sure JavaScript is enabled. If your browser blocks the embedded player, open the game directly. Sound may need a tap or keypress before your browser allows it.
Is this an official UNDERTALE game?
No. UNDERTALE and its characters belong to Toby Fox. The simulator was created by Jcw87. This is an independent fan website, not affiliated with or endorsed by Toby Fox.