CryptoKitties: A Pioneer in Ethereum Gaming and NFTs

What Is CryptoKitties?

Launched in 2017 by Axiom Zen, CryptoKitties is an Ethereum-based game that allows you to buy, sell, and breed collectible digital cats, and was an early and highly publicized example of non-fungible token (NFT) technology in action. CryptoKitties was designed to introduce new users to blockchain technology in an accessible and gamified way akin to card-based trading games like baseball cards or Magic: The Gathering. Every CryptoKitty is a unique NFT, coded to ERC-721 token standards, and has a set of “genes” that determine its appearance, which can be passed onto offspring by “breeding” CryptoKitties with one another.

At its peak in 2017, CryptoKitties attracted more than 14,000 active users daily and propelled Ethereum technology to the forefront of the gaming industry for the first time. Smart contract technology and provably rare digital assets in the form of NFTs have helped grow Ethereum gaming into one of the most exciting sectors in blockchain, as evidenced by platforms like Nifty Gateway, OpenSea, Rarible, and NBA Top Shot. Now, CryptoKitties can also be used throughout the growing landscape of Ethereum-based games, including on platforms like Decentraland, KotoWars, and Heaven.cat. To play with CryptoKitties, all you need is a computer that runs Chrome or Firefox, a cryptocurrency wallet like MetaMask or Dapper, and ether (ETH) to pay for fees and trades.

Where To Buy CryptoKitties

After setting up your cryptocurrency wallet, you can explore the CryptoKitties marketplace to find Kitties for sale. Each Kitty has a name, bio, and price (in ether). Additionally, every Kitty has “cattributes” or unique genetic traits — such as eye shape, eye color, and fur — that determine its appearance, and a generation that indicates when they were created. Some traits are more rare than others, and early-generation Kitties tend to be more valuable than later-generation Kitties. If you find a Kitty that you would like to purchase, you can click “buy now” to take ownership of the digital asset immediately. Alternatively, you can make an offer of your choice to the Kitty’s owner, who can choose whether to accept or decline. Offers can be made on any Kitty in the game — not just the Kitties for sale in the marketplace.

You can create a new Kitty by breeding two of your own Kitties or by using a “public sire,” which is a Kitty made available for breeding by its owner. Every time you breed a Kitty, you are required to pay a fee of 0.008 ETH, in addition to a transaction fee that varies based on Ethereum network congestion. Public sires charge additional breeding fees. Each Kitty has a “cooldown speed” — a mandated resting period that occurs after a Kitty has been bred. The period ranges from one minute to one week, and the more kittens a Kitty produces, the slower its cooldown speed will be. If you wish to sell your Kitty, you can create an auction, which will make your Kitty available in the marketplace. You can select the starting bid, final price, and the duration of the auction.

The Technology Behind CryptoKitties

Each Kitty is an ERC-721 token — also known as an NFT — that is indivisible and unique. ERC-721 tokens like CryptoKitties, which are only found on the Ethereum blockchain, are provably rare, meaning that their underlying code helps ensure that their validity is unique. Ethereum utilizes smart contracts to control the distribution of Kitties and track their ownership. More specifically, the Core CryptoKitties Contract tracks ownership, ownership transfers, and approved siring. Smart contracts also keep track of Kitty genes and facilitate sale and breeding auctions. Each action, such as breeding, buying, and selling is a transaction executed by smart contracts and requires a transaction fee. Because Kitties are tokens on the blockchain, they can be transferred easily and will continue to exist as long as the Ethereum blockchain exists — even if the CryptoKitties website shuts down.

At the time of CryptoKitties’ launch in late 2017, Initial Coin Offerings (ICOs) and scams dominated media reporting on the blockchain industry. CryptoKitties changed public perception of the blockchain industry by introducing one of blockchain’s earliest non-financial use cases and pioneering the ERC-721 token standard. The game became so popular upon launch that its volume of transactions congested the Ethereum network for a number of days, an event that highlighted the scaling challenges of Ethereum at the time. The incident led to a number of innovative solutions for managing transactions on the Ethereum platform, and helped inspire a number of Layer-2 Ethereum scaling solutions that have become essential pillars of the blockchain ecosystem's exciting wave of development.

By creating one of the first fun, accessible blockchain-based games, CryptoKitties introduced countless new users to blockchain technology while demonstrating the technology’s potential through a lighthearted but important application. CryptoKitties is a pioneer in NFTs and Ethereum gaming, and its success has propelled the blockchain ecosystem forward in both technology and adoption.