I am going through the Cryptokitties code, which does not include the optional Enumerable contract, but the KittyBase contract basically declares equivalent indexation and functions. Why did Cryptokitties roll out their own mechanics?

1 Answer 1


Cryptokitties was deployed on 2017-11-28, which is a few months before the ERC721 spec got its first commit and only two months after the ERC721 spec even got drafted.

Because of this, Cryokitties had to implement ERC721 prior to the spec being complete, which is why they may not include certain, expected functionality.

With that said, Cryptokitties helped pioneer the standard and got it to where it is today.

  • Correct I've now been through a full update of Cryptokitties contract to Solidity 0.6, and most of the Cryptokittie code is now in the core ERC721 contract. Thanks. Commented May 16, 2020 at 13:37

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