Repeated Prisoner’s Dilemma Simulator
One tempting move can change what happens next. Choose two strategies, keep the partners together, and follow their choices and payoffs — round by round.
Prisoner’s dilemma · 12 rounds
Link to this comparisonPlayer 1 · Tit for tat
11 points
Cooperated in 1 of 12 rounds
Player 2 · Always defect
16 points
Cooperated in 0 of 12 rounds
How the points accumulate
━ Player 1┄ Player 2
Player 1: Defect · Player 2: Defect
When cooperation holds — or breaks
C = cooperate · D = defect. Choose a round to inspect it.
Player 1 on top · Player 2 below
Every round: actions and exact payoffs
| Round | Player 1 | Player 2 | This round | Total |
|---|---|---|---|---|
| 1 | Cooperate | Defect | 0 / 5 | 0 / 5 |
| 2 | Defect | Defect | 1 / 1 | 1 / 6 |
| 3 | Defect | Defect | 1 / 1 | 2 / 7 |
| 4 | Defect | Defect | 1 / 1 | 3 / 8 |
| 5 | Defect | Defect | 1 / 1 | 4 / 9 |
| 6 | Defect | Defect | 1 / 1 | 5 / 10 |
| 7 | Defect | Defect | 1 / 1 | 6 / 11 |
| 8 | Defect | Defect | 1 / 1 | 7 / 12 |
| 9 | Defect | Defect | 1 / 1 | 8 / 13 |
| 10 | Defect | Defect | 1 / 1 | 9 / 14 |
| 11 | Defect | Defect | 1 / 1 | 10 / 15 |
| 12 | Defect | Defect | 1 / 1 | 11 / 16 |
Try a single action flip against tit for tat, then grim trigger. Does cooperation return? Compare the history, not just the final score.
Rules and limits of this experiment
The same two players choose simultaneously every round. They see both actual actions after each round. Payoffs add without discounting. The game ends after the chosen number of rounds.
These fixed rules do not reason about the last round or learn new strategies. This is one deterministic matchup, not a tournament, an equilibrium solver, or evidence of a universally winning strategy. The optional flip is a chosen intervention, not a sampled error rate.
- Always cooperate
- Cooperate every round.
- Always defect
- Defect every round.
- Tit for tat
- Start by cooperating. Then copy the other player’s last action.
- Grim trigger
- Cooperate until the other player defects once. Then always defect.
- Alternate
- Start by cooperating, then alternate defect and cooperate.
For a teaching precedent: Carleton’s repeated-game exercise. This tool implements the rules listed here.
Review your exact payoff matrix, then save a private lesson. Students make their own choices in two rounds with the same partner. Automated strategies, round count and action flip do not transfer.