Each round, two players secretly choose to COOPERATE or DEFECT. Cooperating builds mutual profit; defecting steals a bigger cut — but only if the other player stays naive. Played once, defection rules. Played over and over against the same opponent, something much more interesting happens.
they C
they D
you C
+3 / +3
+0 / +5
you D
+5 / +0
+1 / +1
// your strategyrules check top-down · first match acts
load a classic recipe:
> on round 1 there is no history yet: “copy their last move” cooperates, “do the opposite” defects. Your strategy is saved in this browser.
// meet the field
noise = a move sometimes flips by accident. Try 5% and watch grudges become death spirals.
// round-robin — everyone plays everyone (self included, like Axelrod 1980)
// single match — watch it play out move by move
vsspeed
0
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0
// evolution — each generation, the bottom 4 die and the top 4 reproduce
// trust trials — prove your strategy under pressure
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VS
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> Inspired by Robert Axelrod's 1980 computer tournaments — where the simplest entry, Anatol Rapoport's TIT FOR TAT, beat every clever program — and by Nicky Case's “The Evolution of Trust”. The lesson survives noise, evolution and forty years: be nice, retaliate, forgive, don't be envious.