What Is CryptoKitties? The Game That Clogged Ethereum

CryptoKitties is a blockchain game launched on Ethereum in November 2017 where players buy, collect and breed digital cats. Each cat is a unique non-fungible token (NFT). It was built by Vancouver studio Axiom Zen, which later spun out Dapper Labs. Within weeks of launch it was congesting the Ethereum network, and its code helped shape ERC-721, the standard most NFTs still use. The original Ethereum game still technically works, but trading is thin. On 24 October 2026 the cheapest kitty on OpenSea was listed at about 0.0005 ETH, roughly $1.28.

Key takeaways

• CryptoKitties went live on 28 November 2017. By December it was a major share of Ethereum traffic, and transaction fees and delays rose sharply.
• Its contract was cited as prior art in EIP-721, the NFT standard co-authored by Dieter Shirley of the CryptoKitties team.
• Dapper Labs went on to build the Flow blockchain and NBA Top Shot. In 2026 the CryptoKitties brand lives on mainly as a Flow-powered Telegram game.
• Most old kitties are worth a dollar or two. A handful of rare, early or “fancy” cats still sell for much more.

CryptoKitties history: from hackathon to headlines

Axiom Zen first showed CryptoKitties at the ETH Waterloo hackathon in October 2017 and launched it publicly on 28 November 2017, after a short closed beta. The idea was deliberately playful: a collectible game that would get ordinary people to set up a wallet and send an Ethereum transaction.

The December 2017 Ethereum congestion

Every CryptoKitties action was an on-chain transaction: buying a cat, breeding two cats, or listing one for sale. When the game went viral in early December 2017, those transactions flooded the network. Wikipedia’s account says the game made up as much as a quarter of Ethereum traffic at its peak. Pending transactions piled up, gas prices jumped, and unrelated users, including token-sale participants, waited hours for confirmations. Miners responded by raising the block gas limit.

It was an early stress test that showed how little capacity Ethereum’s base layer had for consumer apps. That lesson pushed developers toward later scaling work: sidechains, rollups, and eventually Dapper’s decision to build its own chain.

How the CryptoKitties game works

Each kitty has a “genome” stored on-chain. The genome determines visible traits such as fur pattern, eye shape and colour, plus hidden recessive genes. The artwork itself is stored off-chain by the company.

• Gen 0 cats. The contract released one new “generation 0” cat every 15 minutes for the first year. That was the only supply that didn’t come from breeding.
• Breeding. Any two cats can breed. Neither has a fixed gender, and each can act as either parent. The offspring’s generation is one higher than its highest-generation parent, and its traits mix the parents’ genes, sometimes surfacing rare “mewtations”.
• Cooldowns. Each breeding increases a cat’s cooldown, up to a maximum of one week. Low-generation cats with short cooldowns are therefore scarcer and more valued.
• Siring. Owners can rent a cat out as a sire for a fee, creating a breeding market.
• Fancy and exclusive cats. Specific trait combinations unlock limited “fancy” art, and some cats were released only for events. These are the ones collectors still chase.

Over time players bred more than two million cats. OpenSea showed about 2.03 million items in the collection in October 2026. That abundance is the main reason most kitties now trade for very little.

CryptoKitties NFT: why it mattered for ERC-721

Before CryptoKitties, Ethereum tokens were mostly fungible ERC-20 coins. Every unit was the same. CryptoKitties needed a token where each unit was different and individually owned. Its contract became an early working model, and EIP-721 was drafted in January 2018. Dieter Shirley, the CryptoKitties technical lead and a Dapper Labs co-founder, was a co-author. The final EIP lists CryptoKitties as compatible with an earlier version of the standard. It also cites the CryptoKitties contract for design choices such as pausing transfers. ERC-721 went on to power profile-picture collections, digital art and game items. Our what are NFTs explainer covers the standard in more depth.

Dapper Labs and the move to Flow

The congestion convinced Dapper Labs that consumer collectibles needed a chain designed for them. It built Flow, a proof-of-stake blockchain that splits work across specialised node types. It used Flow to launch NBA Top Shot, which became far larger than CryptoKitties in trading volume during the 2021 NFT boom. In 2021 the team announced plans to bring CryptoKitties to Flow.

To buy the native token of the chain Dapper Labs built, follow our guide on buying FLOW after the 2025 exploit.

The original Ethereum contract can’t be moved. Existing kitties remain ERC-721 tokens on Ethereum. The brand’s current home is “CryptoKitties: ALL THE ZEN!”, a Telegram game credited as “powered by Flow”. Its official site listed an event update dated February 2026 and mentions Meowcoins as player rewards. It is a separate game, not a revival of the 2017 breeding market.

Are CryptoKitties worth anything?

Mostly no, with exceptions. On 24 October 2026, OpenSea showed a floor price of about 0.0005 ETH (around $1.28), with less than 1% of the collection listed. Floor prices change constantly, so check the live collection page. Value tends to come from:

• Founder cats and very early Gen 0 cats, especially low token IDs.
• Fancy and exclusive cats with limited supply and recognisable art.
• Rare traits and short cooldowns, which matter to the remaining breeders.
• Historical provenance, such as cats tied to famous early sales.

Sales like Dragon’s 600 ETH are history, not a guide to today’s prices. They’re covered alongside other record sales in our most expensive NFTs list.

How to check or sell an old kitty

1. Find the wallet you used in 2017–2018. Many players used MetaMask. You’ll need its seed phrase or private key.
2. Look up the address on Etherscan or OpenSea. Your kitties appear as tokens from the CryptoKitties core contract.
3. Compare your cat’s generation, cooldown and traits with recent sales, not just listings.
4. List it on a marketplace that supports the collection. Factor in Ethereum gas fees, which can be more than a floor kitty is worth.
5. Beware of DMs offering to “buy your rare kitty” through an unfamiliar site. That’s a common wallet-drainer lure.

If you sell for more than you paid, the gain may be taxable. For more collector guides, see our NFT guides hub.

What CryptoKitties teaches about NFT value

CryptoKitties showed both what NFTs do well and where they fail. It proved that verifiable digital ownership and open trading could draw a crowd, and it produced a lasting technical standard. It also showed that unlimited breeding dilutes scarcity, that hype-driven prices rarely last, and that off-chain art and company support still matter.

The economics worked like this. Breeding let players create new cats whenever their cooldowns allowed, so supply grew with the player base. Early buyers profited by breeding and selling to newcomers. Once new arrivals slowed in 2018, there were more cats than buyers, and prices fell for everything except the scarcest cats. Wikipedia’s account notes that by 2022 the game was down to fewer than 100 sales a day. Later play-to-earn games that depended on a steady stream of new players often followed the same path. Before you buy any game NFT, ask who the next buyer will be once the novelty fades, and whether the item still works if the company behind it stops supporting it. The same pattern played out across the wider market. Our piece asking are NFTs dead? looks at where that leaves collectors today.

FAQ

Is the CryptoKitties game still running?

The original Ethereum contracts still work, so kitties can still be bought, sold and bred, but activity is very low. Dapper Labs’ current CryptoKitties product is a separate Telegram game, “ALL THE ZEN!”, powered by Flow, which posted updates in 2026.

Who made CryptoKitties?

CryptoKitties was created by Axiom Zen, a Vancouver studio. It spun the project out as Dapper Labs in March 2018, backed by Union Square Ventures, Andreessen Horowitz and later Venrock. Dapper Labs went on to build the Flow blockchain and NBA Top Shot.

How much did the most expensive CryptoKitty sell for?

The record is “Dragon”, which sold for 600 ETH on 4 September 2018, worth roughly $170,000 at the time. Earlier, the “Genesis” cat sold for about 247 ETH in December 2017. Those prices reflected early-era hype. Today’s floor is around one to two dollars.

Are CryptoKitties on Ethereum or Flow?

The original kitties are ERC-721 tokens on Ethereum and cannot be moved to another chain by the contract itself. Dapper Labs’ newer CryptoKitties experiences, including the Telegram game and Meowcoins, run on its Flow blockchain.

Crypto is volatile and risky; this is education, not financial advice. Do your own research.