I'm totally new to cryptokitties, but my understanding of cryptokitties so far is:

  • It's a smart contract that generates new kitties according to your ethereum address.

My questions are:

  • If you are breeding kitties, how does it handle randomness to "breed" different attributes of kitties?
  • Can we see how the kitties smart contract is made?
  • Can the crypto kitties website run as a standalone app (dapp) to interact with the ethereum blockchain?

2 Answers 2


Partial answer:

A large chunk of the contract can be seen here: https://etherscan.io/address/0x06012c8cf97bead5deae237070f9587f8e7a266d#code

The breeding algorithm is "sooper-sekret" and is handled by a contract that implements GeneScienceInterface. As not-an-Ethereum-developer, I don't know where that contract lives. But @comodoro does! it's at 0xf97e0A5b616dfFC913e72455Fde9eA8bBe946a2B Presumably, the source isn't published and you'd have to reverse engineer how the pseudorandomness is implemented. Also presumably why people from the cryptokitties creators aren't allowed to own the cryptokitties (at least, I read that somewhere): they'd get all the fancy cats!

  • 2
    The geneScience address is now pointing to 0xf97e0A5b616dfFC913e72455Fde9eA8bBe946a2B. Code is not public, someone might try to reverse engineer it, but normal people usually have better things to do.
    – comodoro
    Commented Dec 13, 2017 at 18:04
  • 4
    Reverse engineering is how you learn stuff! :-) See Towards Cracking Crypto Kitties’ Genetic Code. Commented Dec 13, 2017 at 20:00

CryptoKitties is composed of 4 public facing contracts.

In November 2017, as part of their launch, the AxiomZen team put out the CryptoKitty Bounty Program with all the primary smart contracts on github here: https://github.com/axiomzen/cryptokitties-bounty

As part of the bounty program they released the details of 3 of 4 of their primary smart contracts:

You can read more about the CryptoKitties as well as the roles of CEO, CTO, COO and how the bring new Kitties (as well as their features/genotypes/phenotypes) into the world here: https://github.com/axiomzen/cryptokitties-bounty/blob/master/CryptoKitty%20Basics.md#common-functions

  • The thing I don't understand is: I think all contract is published by someway. (i.e: we can search on etherscan). Why we cannot find GeneScience.sol. thanks.
    – hqt
    Commented Apr 18, 2018 at 19:37
  • @hqt: It's the EVM bytecode that's published to the blockchain, not the Solidity source. Etherscan allows smart contract authors to also add their Solidity source code, but they don't have to do this. Commented Dec 4, 2018 at 6:20
  • @EricKigathi the four hashes you mentioned appear to be contracts on rinkeby, do you know the corresponding transaction hashes for the contracts on mainnet? Commented Dec 4, 2018 at 6:26

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