Prisoner’s Dilemma.
Choose cooperate or defect for ten rounds. Your partner follows a rule you can inspect. Compare your score, their score, and what your choices did to the relationship.
Earn as many points as you can in 10 rounds.
- 1Choose a partner.
Read their rule below. It stays the same for all ten rounds.
- 2Choose Cooperate or Defect.
Each click plays one round. Your partner uses past rounds and cannot see your current choice.
- 3Read the result, then choose again.
Points add to your total. After round 10, replay and compare your approach.
There is no fixed score to beat and no strategy that is best against every partner. Your goal is to learn how your choices affect the next round.
Choose who you will play against.
Your partner’s rule is visible. Select one, review the points, then start.
Points for each round
Both cooperateYou get 3 · Partner gets 3
Both defectYou get 1 · Partner gets 1
You defect · Partner cooperatesYou get 5 · Partner gets 0
You cooperate · Partner defectsYou get 0 · Partner gets 5
See a two-round example — not scored
Against Tit for tat: if you defect in round 1, your partner still cooperates. You earn 5 and they earn 0. If you cooperate in round 2, they defect because they copy your previous move. You earn 0 and they earn 5. After those two rounds, the totals are 5 each. This example adds no points to your game.
Why repeated choices matter
In a single round, defecting earns you more for either partner move. Over repeated rounds, your choice can change how a responsive partner treats you next time.
These are fixed opponent rules, not universally optimal strategies. Cooperation can pay with some partners; it is not guaranteed by repetition or by this ten-round exercise.
About Prisoner’s Dilemma
Made by Malav Joshi. A place to practise and understand the decisions behind the game.
Why is it called a dilemma?
In one round, defecting gives you more points for either choice your partner makes. Yet when both players defect, both earn less than if both had cooperated. Individual incentives and the best shared outcome point in different directions.
Does cooperating always win?
No. In this exercise, an opponent’s rule and the remaining rounds matter. Tit for tat responds to your previous move; an always-defect opponent never reciprocates. Repetition can create an incentive to cooperate, but it does not guarantee cooperation or make one strategy universally best.