Rock Paper Scissors online — but the AI studies you
The classic hand game, rebuilt as a free browser game with a twist: your opponent, Sergeant Sandy the crab 🦀, is an adaptive AI that watches how you play and turns your habits against you. No download, no sign-up — it runs instantly on phone, tablet and desktop.
Complete rules
- Rock ✊ crushes Scissors, Scissors ✌️ cut Paper, and Paper ✋ wraps Rock. Matching throws are a draw.
- Controls: 👆 tap 🪨 ROCK 📄 PAPER ✂️ SCISSORS — or press R P S (or 1 2 3) on a keyboard. The hands shake through "Rock… Paper… Scissors… SHOOT!", then reveal together.
- Best of 5: first to 3 round wins takes the match; draws are replayed.
- Endless Streak: wins grow your streak, draws are safe, one loss ends the run — your score is the streak length.
How the AI works (no, it can't see your hand)
Sergeant Sandy uses a small Markov chain — the same idea behind your keyboard's text prediction. Each round it records what you threw after your previous two throws. Next round it looks that pattern up — "after Rock-then-Paper, this player usually throws Scissors" — and plays the counter (Rock). If the pattern is new, it falls back to your one-throw tendencies, then to your overall favourite. A slice of its choices stays completely random so the duel never feels rigged, and it locks its throw the instant you tap yours — it never peeks.
How to beat Sergeant Sandy — strategy tips
- Never repeat a pattern three times. Sandy needs a couple of samples to lock onto a habit — break the chain first.
- Beat your own instincts. Most players repeat a winning throw. Switch after you win.
- After a loss, don't play what just beat you — Sandy expects that rotation. Skip two steps instead.
- Use draws to reset. In Endless mode a draw costs nothing — it's free information about what Sandy expected.
- Play the counter-counter. Thrown Rock twice? Sandy expects a third and will show Paper — throw Scissors.
- When in doubt, be genuinely random — map the seconds on a clock to Rock, Paper or Scissors.
Fun history facts
Rock Paper Scissors is ancient: the Chinese hand game shoushiling appears in writings from the Han dynasty, over 2,000 years ago, and it reached the modern world through Japan as jan-ken. There are official world championships with real prize money, and in 2005 a Japanese firm made Christie's and Sotheby's play a match for the right to auction its $20 million art collection — Christie's won with Scissors.
FAQ
Is this Rock Paper Scissors game free?
Yes — completely free, no download and no sign-up. It runs in any modern browser on phone, tablet or desktop.
Does the AI cheat and see my choice?
No. Sergeant Sandy locks in its throw the instant you tap yours, using only the history of your previous throws. It predicts, it never peeks.
What's the difference between Best of 5 and Endless Streak?
Best of 5 is a short duel — first to 3 wins. Endless Streak is survival: draws are safe, but a single loss ends the run.
How do I save my score?
Your best streak and stats save automatically in your browser's local storage, and you can export a score-card image (9:16 or 16:9) from the results screen.
Can I really beat a pattern-learning AI?
Yes. It only wins if you're predictable — mix your throws, break your habits, and you can out-guess it.