CyptoKitties is a collectible trading game whose objective is to create and collect unique cats. Created by Axiom Zen, a venture studio in Vancouver, Canada, the game was motivated by the core team’s desire to make the Blockchain more fun by creating unique collectible items, specifically cats, which are inherently appreciable. Each kitty is widely accessible to the public yet has one unique owner, and a newly generated kitten’s appearance, everything from eye color to fur pattern, is a product of code and inherited traits. The project was launched October 2017 during a hackathon at ETHWaterloo (the team gave out two breedable Gen-0 kitties to each participant), gained in popularity to the point of clogging the Ethereum network, and, in March of 2018, was spun off into its own company, having raised $12 million from venture capitalists.
CyptoKitties’ objective is to collect unique cats. Players can accomplish this by purchasing kitties through the game’s internal market, trading with other players, or by breeding cats. The base kittens, generated every fifteen minutes, are called Gen 0 cats and have Axiom Zen determined attributes, such as fur pattern and eye color. The game caps Gen 0 cats at 50,000, with the cap reached as of November 2018. The proceeds from sales of Gen 0 cats compensated the game’s developers.
Breeding cats is a core game component. To breed a new cat, two cats are sent into a smart contract that generates a third, which shares some randomly inherited parental traits. A cooldown attribute limits how often a given cat can produce new offspring, and newly generated kitties are of a higher generation than their parents. Determining how to breed kitties with specific combinations of rare attributes, which can be particularly valuable, drives gameplay, and involves considerations of a kitty’s ‘genetic code’, its dominant and recessive traits, the possibility of ‘mewtations’, and an awareness of which combinations of the over 270 unique traits are rarest and most desirable. A .008 ETH fee, paid to the Ethereum chain for smart-contract execution, is the only charge associated with breeding cats.
Each Kitty is non-fungible ERC 721 token. The desirability of a given token is a product of its code’s rarity— ‘cattributes’ combinations drive token price. Notably, token holders do not hold rights to the images associated with the token holder owned code; this means that Axiom Zen can update images without tokenholder consent. While token holders do not own the artwork, they do possess certain rights as specified by the NFT License, such as the right to use the artwork for self-purposes.
Collectible enthusiasts with interests in blockchain were the game’s initial intended users. Axiom Zen has since taken steps to attract a broader user base: the project created an incentive program called KittyVerse to fund development of apps that make use of Kitties. Such apps and other user-created mods have helped sustain interest in the game.