Rethink

Cooperate, or defect?

Describe a strategy for the repeated prisoner's dilemma and we'll code it by hand, or write it yourself in Python. When entries close, it plays every other one.

Enter a strategy Write it in Python
Entries close in  
Points per round: the row player's points first, then the column player's.
They cooperateThey defect
You cooperate 3, 3both rewarded 0, 5you're exploited
You defect 5, 0you exploit 1, 1both punished
0
0
cooperate   defect. A demo match between two house players.

How it works

  1. Enter it

    In your own words, or in Python. You get a ticket number and a private status page.

  2. We code it

    We turn your description into code by hand, or check yours. Your status page shows when it's done.

  3. Everyone plays

    After the deadline, every strategy plays every other one, and a copy of itself.

  4. You get results

    An email with your rank, your score, every match, your best and worst opponents, and how we coded you.

Rules

  • Each match is a series of rounds. In every round both players choose at the same time: cooperate or defect. Points follow the matrix above.
  • A match lasts between 450 and 550 rounds. Nobody knows the exact number in advance, and it's the same for every match.
  • Your strategy can see every earlier move in the match and both scores, and it can use randomness.
  • It plays every entry once, including a copy of itself, plus house players: all 63 strategies from Robert Axelrod's second tournament (1980), ported from their original code, and strategies written by AI models.
  • The highest total score across all matches wins. Beating your opponent in a match doesn't matter, only your own points do.
  • One entry per email address and per network each day (UTC).
  • We'll reject descriptions that can't become a clear strategy, like ones that need to read the opponent's code or know the round count, and code that breaks the code rules. Offensive names are hidden.

Privacy

Your email is used for two messages, your ticket and your results, and is deleted once results are sent. We never store your IP address, only a one-way hash used to enforce the daily limit.

Your strategy name, display name, description and a short note on how we coded it are public: on the leaderboard, and in the matches replayed on this page. The code stays private, whether we write it or you do.