CryptoKitties is a blockchain-based game that uses non-fungible tokens (NFTs) depicting cartoon cats.
Blockchain games have become a standard part of the broader crypto industry. Like decentralized finance (DeFi), they account for a significant portion of on-chain interactions. Whole financial mini-markets have cropped up around play-to-earn (P2E) games like Axie Infinity, which have the potential to generate such meaningful profits for players in lower-income countries that about 35% of its traffic came from The Philippines in 2022.
Before the hype began, one blockchain game started it all.
CryptoKitties was introduced in 2017 as a game that used non-fungible tokens (NFTs) as tradable “in-game” assets. Users can not only buy and sell their Kitties on the open market, but they can also breed them to create new NFTs with desirable attributes.
CryptoKitties was launched on Ethereum, and its popularity famously caused intolerable congestion of the chain, driving up transaction fees and driving down transaction speeds. It has since transitioned to the purpose-built Flow blockchain, which was created by CryptoKitties’ developers at Axiom Zen. It now is one of many blockchain games in the space—and perhaps one with simpler gameplay when compared with its company—but it remains an archetype of the blockchain game.
How was CryptoKitties developed?
CryptoKitties was conceptualized and launched by a Canadian tech start-up called Axiom Zen, which was founded by Rohan Gharegozlou. He earned both his Bachelor’s and Master’s degrees from Stanford University before moving on to the venture capital world. He founded Axiom Zen in 2012. One of the company’s earliest projects was ZenHub, which meant to improve upon the services offered by GitHub.
In October 2017, Axiom Zen announced CryptoKitties. Within 3 hours of the launch of its beta version, CryptoKitties became the third most active decentralized application (dapp) on Ethereum. Ethereum founder Vitalik Buterin’s own father was an early proponent of the project, which undoubtedly helped drive community enthusiasm.
Within two months of its soft launch, some CryptoKitties NFTs were worth more than $100,000 on the project’s marketplace. By early December 2017, almost $4.5 million had been transacted in cat NFTs, and the number of pending transactions on Ethereum multiplied by more than five times—in no small part due to CryptoKitties. The creators, much like Ethereum’s blockchain, were not ready for their project’s immediate popularity. But this meteoric rise allowed Axiom Zen to raise $12 million in a funding round soon afterwards.
Axiom Zen spun out Dapper Labs to run CryptoKitties and develop NFT collections including NBA Top Shots and UFC Strike. The new company would also guide the development of the Flow blockchain, which was built as a scalable layer 1 alternative to Ethereum and now supports Dapper Labs’ NFT-based projects.
How does CryptoKitties work?
CryptoKitties are on-chain assets like cryptocurrencies and other NFTs. They were built on the ERC-721 token standard and are governed by a smart contract. The project is now managed by Dapper Labs.
General concepts: collecting and trading
CryptoKitties took an old idea and ported it over to the blockchain space. Perhaps that explains its impressive success. It has been compared to many historical collectable crazes, but one of the most common is Beanie Babies, which thrived in the mid- to late 1990s. Because of their digital footprint and ability to have them breed/interact (see below section), it has also been likened to a modernized version of Tamagotchi digital pets.
Kitties are made up of various “cattributes,” which include eye shape, eye color, fur, mouth, environment, and more. Each Kitty has a primary gene for each of these cattributes, and this is what is expressed in how the Kitty looks. Meanwhile, there are three hidden genes for each cattribute, and although these are not displayed, they can be passed onto the cat’s offspring. In a way, this approximates real genetics, which involves dominant and recessive genes. There are billions of possible combinations.
A cat’s collective cattributes, along with its relative age/generation, define how rare it is. Third party websites have been built to help collectors understand how rare certain traits and Kitties are. And as with all things collectible, a Kitty’s rarity defines how much it is worth. There are also Fancy Cats, Exclusive Cats, and Special Edition Cats that are rare and have desirable traits. Kitties can be bought and sold among collectors.
Breeding and siring
Aside from trading Kitties, collectors can also breed them. Every Kitty can play the role of either Sire or Dame, with the Sire providing genetic material and the Dame becoming “preggers” and ultimately birthing a new cat NFT. Cat-herders can breed two of their own Kitties together, or they can choose a Sire from the public marketplace.
Generally, cats with desirable traits are listed as potential Sires by users as a way to give others a chance to breed those traits into their own NFTs. This costs a fee, which is paid to the owner of the Sire.
After a new Kitty is generated through breeding, there is a “cooldown” period in which the parent Kitty cannot breed. These times range from fast (1 minute) to catatonic (1 week). Kitties from earlier generations start with shorter cooldown times, whereas those from later generations—the result of many episodes of breeding—have longer cooldown times.
As stated above, breeding allows for new Kitties to be formed based on the combination of their parents’ traits. However, sometimes genes will mutate, and an offspring Kitty might end up with an unexpected trait.
Cryptokitties essentials
CryptoKitties is a blockchain-based game that uses cat-themed non-fungible tokens (NFTs).
One of original blockchain games, CryptoKitties launched in 2017 and quickly became so popular that it caused congestion of the Ethereum network, such that now it has moved to the Flow blockchain.
The gameplay and economy of CryptoKitties rely on “cattributes,” which are traits displayed by the cat NFTs. These are defined by the CryptoKitties smart contract and are defined in future generations through breeding.