CryptoKitties is a game built on the Ethereum blockchain in which users can collect and trade digitally scarce virtual cats.


CryptoKitties is a blockchain based game in which users collect and trade digitally scarce virtual cats using ETH tokens. Each kitty has unique 256-bit genome which defines it's appearance and traits. Players are able to breed new kitty who inherit traits from their parents genome. AxiomZen developed the game including the five smart contracts which allow users to interact with the Ethereum blockchain. The blockchain tracking of the CryptoKitties means that the kitties are permanently and immutable available on the blockchain regardless of the original creators continued support of the project. CryptoKitties is a new type of digital asset known as a cryptocollectables, other examples include CryptoPets, CryptoPuppies.


Supply and breeding

The supply of kitties is limited based a fixed number of new kitties called Gen 0 kitties released every fifteen minutes. Additionally, users can choose a mother and father to breed a genetically unique offspring. The rate at which users can breed new kitties is limited, and users also have to pay a fee to breed.


Each kitty has a unique genome represented by a 1 or a 0 at each position of their 256-bit genome. The exact genome of the kitty is stored on the blockchain represented by this string of bits. This genome determines the properties of the kitty such as background color, breeding cooldown time, whiskers, beard, and others. Players can sire a new offspring from a chosen set of parents. This is done by a genetic algorithm which mixes the genetic data from the parents as well as info from the ethereum block hash to create a unique offspring. The offspring may have unique or desirable properties to players which make them more desirable for trading on the Cryptokitties marketplace.

A cracking program was developed which allows users to determine the exact genes of the offspring for a given 256 block time segment. If the user doesn't like that specific gene set they could wait 256 blocks and get another iteration based on the block hash and so on until they arrived at a desired gene set.


Buying and selling of cryptokitties occurs on a marketplace using the digital wallet called MetaMask.


By December 3, 2017 more than $1 million dollars worth had been transacted through the game and was the most popular decentralized application on the Ethereum network, responsible for 15% of all traffic. The network congestion caused by the game highlighted the blockchain scalability issues for the Ethereum network and blockchains in general.


March 20, 2018

Union Square Ventures invests in CryptoKitties

Fred Wilson announces on the USV blog that Union Square Ventures invested in a CryptoKitties funding round. 


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Further reading


Do You Really Own Your CryptoKitties?

Greg McMullen

How a Hackathon Birthed the CryptoKitties Origin Story

Rachel Wolfson

How does work?

Aidan Breen

Introducing 'CryptoKitties,' the New Digital Pets Taking Ethereum by Storm

Joseph Hincks

People have spent over $1M buying virtual cats on the Ethereum blockchain

Fitz Tepper

Response to "Do You Really Own Your CryptoKitties?"

Mack Flavelle

The ethereum world is now obsessed with breeding cartoon cats

Joon Ian Wang

Towards Cracking Crypto Kitties’ Genetic Code

Mo Dong

Documentaries, videos and podcasts