created_at2024-04-24 04:06:26.47321
updated_at2024-05-08 19:24:21.893469
descriptionThe COUP game implemented in the CLI
Dominik Wilkowski (dominikwilkowski)



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This is a coding game where, bots you build, play the popular card game COUP.

You write a bot to play COUP against other bots and tweak its behavior until you find a winning strategy.

This works best if you buy the physical card game and play it a couple times maybe during your lunch break

The idea is to have three rounds of (1,000,000) games to find the winner (sum all scores). Between each round you have time to make adjustments to your bot.

How does this work?


  1. No changes to engine
  2. Name of bots don't change between rounds (so you can target specific bots)
  3. No data sharing between games within a round
  4. No file access to other bots
  5. No changing other bots
  6. No internet access or calls to OpenAI
  7. Do not output to stdout or stderr


Each game is a zero-sum-game in terms of score. That means the amount of negative points given to losers + the amount of positive points given to winners equals to zero.

The score is determined by the number of players (can't be more than 6 per game) and winners (there are instances where the game can stall in a stale-mate which the engine will stop and nominate multiple winners for). Each game will take a max of 6 bots that are randomly elected. Those who win get a positive score, those who lose will get a negative score.

  • Score for losers: -1/(players-1)
  • Score for winners: ∑losers/winners

How to run the game

You can run the game in two modes: play and loop.

Play mode

The play mode will play a single game and nominate (a) winner(s) at the end.

use coup::{
	bots::{HonestBot, RandomBot, StaticBot},

fn main() {
	let mut coup_game = Coup::new(vec![

Loop mode

The loop mode will play n amount of games and sum all score and nominate (a) winner(s) at the end

use coup::{
	bots::{HonestBot, RandomBot, StaticBot},

fn main() {
	let mut coup_game = Coup::new(vec![


How do I build a bot

Implement the BotInterface and override the default implementations of each of the methods you'd like to take control over. The default implementation are the methods of the StaticBot which only takes Income and is forced to coup by the engine if it accumulated more or equal to 10 coins. It does not challenge, counter or counter challenge.

The simplest way to build a bot by falling back to static behavior for each method would be:

use coup::bot::BotInterface;

pub struct MyBot;

impl BotInterface for MyBot {
	fn get_name(&self) -> String {

(This is what the StaticBot is.)

From there you can choose which, if not all, of the below methods you change to make this bot your own.

Methods of the bot

The methods of BotInterface that will define the behavior of your bot.

  • get_name – Called only once at the instantiation of the Coup game to identify your bot
  • on_turn – Called when it's your turn to decide what to do
  • on_auto_coup – Called when you have equal to or more than 10 coins and must coup.
  • on_challenge_action_round – Called when another bot played an action and everyone gets to decide whether they want to challenge that action.
  • on_counter – Called when someone played something that can be countered with a card you may have.
  • on_challenge_counter_round – Called when a bot played a counter. Now everyone gets to decided whether they want to challenge that counter card.
  • on_swapping_cards – Called when you played your ambassador and now need to decide which cards you want to keep.
  • on_card_loss – Called when you lost a card and now must decide which one you want to lose

The context

Each function gets context passed in which will contain below infos:

key description
name Your bots name after it was de-duped by the engine. This means if you have multiple bots with the same name they get a space and a number appended to their name which is used as an identifier
cards Your cards/influences you still have
coins Your coins
playing_bots A list of all playing bots this round
discard_pile A list of all discarded cards so far in the game
history A list of each event that has happened in this game so far
score The current score of the game

How does the engine work

The engine enforces all the rules laid out by the game as best as it can. In areas where the rules are fuzzy or impossible to enforce in a computer world it does best effort to come close to the real world game.

The algorithm

match action
	Assassination | Stealing
			- challenge round
			- counter from target
			- counter challenge
			- action
	Coup | Income
			- action
			- counter round from everyone
			- counter challenge round
			- action
	Swapping | Tax
			- challenge round
			- action


There are two different kind of challenges we distinguish for bots:

  • A challenge to an action
  • A challenge to a counter action

Because the rules of the game state challenges can be called by anyone (the order is never articulated) and because the engine can't call all bots at the same time, the engine will go one by one from the bot whos action just triggered the challenge.

So If player A plays an action then the first bot asked if they want to challenge this is player B. If player C does the action the first bot will be player D.

Perhaps best visible in the test.

Targeting other bots

Because some actions require you to tell the engine who you'd like to inflict this action upon, the engine expects you to give it a name. This name is derived from each bots get_name method. The engine makes sure that there are never multiple bots with the same name by adding a space and a number at the end of duplicate names at the instantiation of the game.

So if we have this list of bots:

  • Tici
  • Bob
  • Clara
  • Bob

The engine will change the names to:

  • Tici
  • Bob
  • Clara
  • Bob 2

These names are then communicated to you via the context struct.

Auto couping

The rules state that if a player has 10 or more coins they have to coup the next time it's their turn. The engine enforces this by calling the on_auto_coup method instead of the on_turn method when it's the bots turn.


The engine will check what a bots plays is legal. If a bot plays an action it can't due to insufficient funds (couping or assassination) it will penalize this bot by taking a card from that bot (and ask the bot which one by calling the on_card_loss method).

The same happened if a bot returns an action with an invalid target (a name of a bot that does not exist).



Fixed engine to check if a target bot not just exists but also is in play. Before a bot could have targeted another bot who is not playing in this round (where we have more than 6 bots) which could have resulted in a panic as these bots may not have 2 cards.


Challenges and counter challenges are not more fair by making sure the first bot being asked for a challenge is the bot next in line according to the bots position. This way for every challenge-able action our counter action the first bot is different and not, as before, the first bot in this game.


Initial release of new rust engine

Commit count: 91

cargo fmt