Sell your crypto collectibles without paying gas!

by Devin Finzer

Here at OpenSea, we’ve been excitedly watching the Ethereum decentralized app ecosystem evolve. New projects launch every week. Some are experimenting with inter-game gameplay, while others are bringing brand new game mechanics onto the blockchain. In this evolving space, a key driver of user adoption is gas prices: the more activity on the network as a whole, the more users have to pay per transaction. Over the last few weeks, gas prices as high as 100 gwei (about $1 per transaction at the time) have stifled user engagement with decentralized applications 💸.

As a marketplace for crypto collectibles, it’s our mission to provide the best experience for buying and selling items, while preserving the trust-less nature of our exchange. To address this problem, here’s what’s in our latest upgrade:

For Sellers

Sell items without paying gas

Now you can auction an item without paying any gas*. Instead of executing an on-chain transaction (which costs ETH to pay for gas), you simply sign a message digitally, which is later “settled” on-chain by the buyer of the item.

For sellers who want to sell a large number of items, the overall cost is dramatically reduced. We spent a lot of time working through edge cases for each asset type so that you spend as little gas as possible. When selling twenty different CryptoStrikers, for example, OpenSea reduces the gas cost by 95%. The savings climb even higher if you find yourself cancelling your expired auctions, which is no longer necessary…

Expire auctions automatically

Now your auctions truly expire! When you set a duration for a declining price auction, it will automatically cancel itself once the specified duration ends. In escrow-based marketplaces, you have to pay gas to cancel auctions, even those with a specified duration. This includes reducing the price on auctions you set too high, which is now a click away…

Instantly adjust your price

We’re also introducing a system for allowing users to more easily adjust prices for their items without having to transact on the network. While increasing the price of an item does require an on-chain transaction (because you’ll need to ensure the smart contract knows that you’re no longer willing to sell at that low price), adjusting the price downward does not require an on-chain transaction.

Users can instantly and freely reduce the price of an item if they find it’s not selling at the current price. All it requires is a digital signature to make a new sale.

Continue using an item while it’s on sale

As mentioned in our post on our new bidding system, we’ve worked hard to make the exchange of items on OpenSea wallet-to-wallet. This means that the item will remain in a user’s account (and be available for gameplay) while it’s on sale. The migration of sell orders off-chain completes our transition to a fully wallet-to-wallet exchange system.

Which items are supported?

Gas-less auctions on OpenSea work for almost all non-fungible tokens. Here are some of the Mainnet asset types that are currently supported, with more being added all the time.

  • CryptoKitties — the game that started it all. Breedable, collectible, and oh-so-adorable cats, each one-of-a-kind and owned by you. They cannot be replicated, taken away, or destroyed.
  • Decentraland — a virtual reality platform powered by the Ethereum blockchain. Users can create, experience, and monetize content and applications.
  • Crypto Space Commander — a space MMO that operates in a completely real-time, player-controlled economy.
  • CryptoStrikers — users can buy, sell, or trade soccer player cards like traditional collectibles, fully confident that the blockchain will track ownership securely.
  • Eth.Town — become a realtor buying out floors for certain crypto-companies in a crypto-business tower.
  • CryptoBots — a battling game centered around cryptographically unique collectible bots.
  • Cryptovoxels — a virtual world on the Ethereum blockchain. Build, develop and sell property. You own your own land, with your ownership recorded permanently on the blockchain.
  • Mythereum — a multiplayer digital trading card game built on the Ethereum blockchain where players build unique decks of collectible cards and challenge others to engage in battle.
  • MakersPlace — the easiest way to create and sell unique digital creations.
  • CryptoArte — A NFT and art collection, CryptoArte projects the Ethereum blockchain history into colorful, unique, and meaningful paintings. Each token represents a given painting and matches its hash on-chain. Token owners can download their painting’s full digital images and order signed, ready to hang prints at cryptoarte.io.
  • CryptoFighters — cryptographically unique collectible fighters on the Ethereum blockchain. Collect, battle and level up your fighters to win new fighters!
  • CryptoMasterpieces — the first platform for collecting one-of-a-kind digital masterpieces. Collectors can buy, sell and trade famous artwork.
  • CryptoCrystal — sentient crystals that have personalities similar to humans while being cute like pet animals.
  • CryptoCelebrities — a popular game involving celebrity trading cards, which are still being traded and used in follow-up games.
  • CryptoRacing — race rare, collectible cars.
  • Cryptogs — Whip out your slammer and get rad on the blockchain! Born at ETHDenver, Cryptogs is the game of pogs on Ethereum.
  • DigitalArtChain — Publish your own digital art on the blockchain. Digital Art is published on IPFS, enabling you own, sell, and purchase published digital art.
  • PandaEarth — Each panda comes from descendants of 50 giant pandas that have been officially licensed by China Panda Conservation and Research Center to breed on the blockchain. Its image, purity and personality is one-of-a-kind and 100% owned by you; it cannot be replicated, taken away, or destroyed.
  • John Orion Young — a contemporary artist living in San Francisco. Classically trained from childhood in his father’s art studio in painting and sculpting, JOY’s mediums today have evolved to include virtual reality, blockchain, and AI.
  • Etheremon — simulates a world of Ether monsters you can capture, transform.
  • SuperRare — a smart contract platform that allows artists to release limited-edition digital artwork tracked on the blockchain, making the art rare, verified and collectible.
  • Known Origin — brings together blockchain technology and digital artwork though the power of ERC721 backed digital arts assets.
  • Gizer — a real-time platform providing opportunities to gamers, hosts and services.
  • HiPrecious — high-end crypto-collectibles, luxuriously made in Paris.
  • HyperDragons — breedable dragons ready for battle.

Notes to Developers

If you’d like to make sure your tokens support gas-free and escrow-free auctions (sell orders), you can follow our tutorial, or simply have your contract inherit from the OpenZeppelin ERC721 standard. Sell orders require the existence of the transferFrom method, and if your contract supports setApprovalForAll and isApprovedForAll, users will only have to make one transaction to approve all your items for trading.

An immediate win for your users

We rolled this feature out for all ERC721-compliant assets. As a developer, if your items are listed on OpenSea, your dapp’s users will automatically be able to sell their items without paying gas. One benefit of using OpenSea as your marketplace is that any future upgrades and features we build are immediately available to your users!

Programmatic sales using the OpenSea SDK

We’ll soon be launching an SDK for buying and selling on OpenSea. Contact us if you’d like access — it’s currently in private beta.

How we did it

As mentioned, we’re building new exchange functionality on top of the Wyvern protocol. Wyvern is a robust, extensible, and security-audited protocol for non-fungible asset exchange. Another huge thanks to the Wyvern team for working closely with us.

Got questions?

Check out our developer tutorial and documentation, or chat with us on our active Discord server!

* As a first time user, you’ll need to complete one preliminary transaction to set up your account, and another to allow access to items of a certain “type” (for example, CryptoStriker cards). Once these initial transactions are completed, however, you can auction any collectible of that type without paying gas. (Some older types of collectibles, including CryptoKitties, require this approval transaction for each item instead of all at once.)

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