CryptoKitties is a breakout application built on the Ethereum blockchain, and it’s taking over the crypto world.
Crypto users are going crazy for the virtual cat game, which features collectible kittens with a real-world value.
The application bridges the gap between the Ethereum “world computer” and a mainstream audience, thanks to its wide appeal and simple user interface.
If you’re interested in the kitty craze, or in Ethereum, the game and its blockchain mechanics are detailed below.

Game mechanics

CryptoKitties lets users purchase collectible kitties with Ethereum, and then breed them to create more kitties.
Each cat has its own genetics which are inherited from its parents and stored in a 256-bit hexadecimal number.
These genes exhibit themselves as “Cattributes”, which define how a cat looks.
Cattributes define colour, expression, body type, and furriness of a CryptoKitty – and players breed kitties to develop rare Cattributes.
Kitties are genderless and can act as either the dad or mom in a breeding pair.
Players can also breed their cats with those of other players, selling the “siring services” of their digital cat for Ethereum.


Cats are bought, sold, and bred using Ethereum, and CryptoKitties interacts with the Ethereum blockchain to function.
The kitties are unique tokens which are encoded on the blockchain as 256-bit numbers and can be sent to any Ethereum address.
The CryptoKitties game runs on the blockchain and comprises five smart contracts running on the Ethereum network.
This means your CryptoKitties do not rely on a central server or authority for their value and issuance, and may exist on the blockchain forever.
To get started with CryptoKitties, you will need to install the MetaMask extension, which acts as an Ethereum wallet in your web browser.
You will then need to purchase or access Ethereum from a cryptocurrency exchange and send it to your MetaMask wallet to get started.


CryptoKitties has become wildly popular since its launch at the start of December and during peak times it accounts for over 15% of all transactions on the Ethereum blockchain.
Players have spent almost $5 million buying kitties on the platform, with rare cats traded for over $10,000 and the smart contracts that make up the game’s codes flooded with transactions.
This has caused a dramatic slowdown on the Ethereum blockchain, with transactions taking up to 20 minutes to be processed – and minimum transaction fees increasing to around $0.25.
While the success of CryptoKitties is great for consumer Ethereum adoption, the stress it has placed on the blockchain means developers face more pressure to implement a scaling solution.
Raising the miner gas limit can alleviate transaction bottlenecks in the short-term, but long-term scaling for Ethereum will only come from solutions like proof-of-stake or sharding.