An OpenSea clone is an open NFT marketplace where anyone can list tokens from almost any collection on the chains it supports. This guide explains how OpenSea works, which parts a copy must rebuild, and what the work costs in time and people.
OpenSea has three core parts. Sellers sign orders off-chain, and a shared contract called Seaport settles a trade on-chain only when someone buys. An indexer reads every collection on the supported chains, and a trust and safety team keeps scams and stolen items out of search results.
How the NFT marketplace OpenSea works
OpenSea launched in 2017 and became the main venue for Ethereum NFTs during the 2021 boom. OpenSea does not choose who can sell. Its indexer picks up any ERC-721 or ERC-1155 contract on a supported chain and builds a collection page from on-chain events and token metadata, and holders can then list their tokens.
Curated venues such as SuperRare work the other way: SuperRare chooses its artists, and Foundation did the same until it shut down. Vertical marketplaces serve one game or one brand. OpenSea combines a search engine with an exchange for every NFT on its chains.
The order protocol: from Wyvern to Seaport
OpenSea first used the Wyvern protocol. In 2022 it moved to Seaport, an open-source settlement protocol that OpenSea wrote and published, and the current release is Seaport 1.6. It contains most of the features a modern NFT exchange needs:
- Offer and consideration items. The offer lists what the maker gives, and the consideration lists what the maker wants and who receives each payment. One order can pay the seller, the marketplace and the creator in one transaction.
- Off-chain signatures. A listing or a bid is an EIP-712 signature that OpenSea stores in its database. Creating a listing costs no gas, and only the purchase touches the chain.
- Criteria-based orders. A buyer can bid on any token in a collection, or on any token with a given trait, because the order holds a Merkle root of the eligible token IDs. Collection offers and trait offers work this way.
- Conduits. A user approves one conduit contract per collection instead of approving each new marketplace contract version.
- Zones. A zone is an optional contract that checks an order when someone fills it, so it can block an item that has been flagged as stolen.
Seaport is open source and is deployed at the same address on many EVM chains. Other marketplaces and aggregators can read and fill Seaport orders, so a new venue shares liquidity with them, which a custom order format would lose. The Seaport repository holds the contracts and documentation.
How a sale and a bid move through the system
A seller connects a wallet and approves the conduit for the collection, which is one on-chain transaction per collection. The seller then sets a price and an expiry date and signs the listing.
A buyer finds the item and sends one transaction, which calls Seaport's fulfill function with the signed order and the payment. Seaport checks the signature, confirms the order is not cancelled or expired, moves the NFT and splits the payment.
A bid works in the other direction. The bidder signs an offer in WETH or another ERC-20 token, because native ETH cannot be pulled from a wallet with an approval. The holder accepts the bid by sending the transaction.
Indexing and metadata
The indexer does most of the work a user never sees. It listens to Transfer events on each chain and fetches the tokenURI metadata, which often lives on IPFS or Arweave. It caches and resizes images, computes trait rarity, and tracks floor prices and volume.
Most of the engineering time on a marketplace goes into this layer. Collections change their metadata after a reveal, IPFS gateways time out, and SVG files can carry malicious scripts, so the media pipeline must clean them before display.
How the market changed after 2021
A marketplace modeled on OpenSea in 2021 would serve a market that has since changed.
Creator royalties
The NFT token standards never enforced creator royalties. EIP-2981 lets a contract report a royalty rate, and each marketplace decides whether to pay it. Blur launched in 2022 with zero trading fees and optional royalties, and many traders moved there.
OpenSea first enforced royalties with an operator filter registry, which collections used to block marketplaces that skipped royalties. In 2023 OpenSea announced that it would retire the filter and make creator fees optional for new collections.
OpenSea now supports royalties that the token contract enforces. ERC-721C and ERC-1155C contracts, created by Limit Break, restrict which operators may transfer a token. OpenSea's help center says Studio collections created after April 2, 2024 can enforce creator earnings, at a maximum rate of 10%. A business that depends on royalties needs that enforcement in the token contract, because a marketplace policy can change.
Professional traders and aggregation
A large share of volume now comes from traders who use aggregators, bulk listings, sweeps and bidding bots. OpenSea bought the aggregator Gem in 2022, and in 2025 it released a rebuilt platform called OS2, designed for faster trading. An open marketplace now needs batch operations, live order book updates and an API that bots can use.
Regulation and trust
The US Securities and Exchange Commission sent OpenSea a Wells notice in August 2024, saying it considered NFTs on the platform to be possible securities. The SEC closed the investigation in February 2025.
Stolen items, fake copies of verified collections and phishing sites that copy the interface are constant problems for open marketplaces.
Fees and tokens beyond NFTs
OpenSea charged 2.5% on sales for years. OS2 cut the fee to 0.5% in 2025, and on September 15, 2025, OpenSea raised the NFT sale fee to 1% on all chains. Its help center lists 1% for NFT sales and 10% for primary mints in a drop.
OS2 also trades fungible tokens, not only NFTs. OpenSea announced a SEA token and set a launch for March 30, 2026, but in March 2026 it postponed that launch for the second time and gave no new date. For 60 days from March 31, 2026, OpenSea also cut token-swap fees on OS2 to 0%.
Features an OpenSea clone needs
| Component | What it does | Build or reuse |
|---|---|---|
| Order protocol | Signed listings, bids, collection offers and trait offers, with one-transaction settlement and fee splits | Reuse Seaport. Write a custom zone only when you need one. |
| Indexer | Reads transfers, mints, metadata and sales, then computes floor price, volume and rarity | Start from a node provider or a commercial NFT API, then run your own cache |
| Media pipeline | Fetches files from IPFS, Arweave or HTTP, converts video, cleans SVG and HTML, serves files from a CDN | Build it, because users see its output on every page |
| Search and discovery | Collection pages, trait filters, sorting and activity feeds | Build on a search engine such as Elasticsearch or Typesense |
| Order book service | Stores signed orders, checks them against on-chain state and removes stale orders | Build |
| Minting tools | Collection creation, lazy minting and drops | Optional at launch |
| Trust and safety | Verified badges, stolen-item flags, spam filters and takedowns of infringing items | Build a process and the tools for it |
| Wallet and payments | Wallet connection, WETH wrapping and an optional card on-ramp | Reuse wallet libraries and a licensed on-ramp provider |
Build sequence for an OpenSea clone
- Choose a narrow market. A copy of OpenSea with no difference gives users no reason to switch. Pick one chain, one asset class or one audience, such as one game's items or one region's artists, and offer better discovery or lower costs there.
- Choose chains. Start with one EVM chain, because each added chain increases indexing work, RPC costs and support load. The page on supporting multiple chains in one NFT product covers the extra work.
- Set up the indexer. Load the history of the collections you need, then follow new blocks and handle chain reorganizations. It usually takes longer to build than the user interface.
- Integrate Seaport. Use the official SDK to create and fill orders, and add your fee recipient as a consideration item. Read each collection's royalty rate through EIP-2981 when the contract supports it.
- Build the order book. Store orders, index them by collection and trait, and remove an order as soon as its maker no longer owns the token or revokes the approval.
- Set up trust and safety before launch. Add verified-collection badges, a report button, a takedown process for IP claims and a feed of stolen-asset reports.
- Audit and test. Any contract you write, such as a zone, a minting contract or a fee splitter, needs an external smart contract audit. Test order fulfillment on a fork of mainnet.
- Publish an API. Traders and aggregators bring liquidity, so publish orders in the Seaport format so other venues can fill them.
Cost and timeline of an OpenSea clone
An OpenSea clone has no fixed price. Four factors set the budget:
- Number of chains. Each EVM chain adds indexing infrastructure and testing, and a non-EVM chain such as Solana, Flow or Cardano needs almost a second product.
- Indexing scope. Indexing a chosen list of collections costs far less than indexing every contract on a chain.
- Custom contracts. With Seaport, the audit covers your integration code, while a custom exchange contract needs a full protocol audit.
- Card payments. Card payments add a payments partner, KYC checks and chargeback risk.
The following figures are an estimate based on the components above, not a quote. A single-chain marketplace on Seaport with an indexer, search, profiles and an admin panel usually takes four to six months. The team is about two backend engineers, one or two frontend engineers, a designer, and part-time DevOps and QA staff. Each extra chain family or custom protocol adds months.
A white-label NFT marketplace launches faster, but the buyer usually gets a weaker indexer and less control over the order book.
What to copy from OpenSea and what to avoid
Copy
- Off-chain signed orders with on-chain settlement, since users now expect to list without paying gas.
- Collection offers and trait offers, which give holders of rarely traded items a buyer.
- An open order format that other venues can fill.
- Fast metadata refresh and correct handling of reveals.
Avoid
- Royalty promises to creators that your contracts cannot enforce.
- Indexing every contract on the first day, which fills search results with spam collections and airdropped phishing NFTs.
- Competing with established venues on fees alone. Blur and OpenSea have both cut fees to zero for periods, and a new venue has less money to spend on zero fees.
- Postponing trust and safety until after launch, because users meet scams on the first day.
The Rarible clone guide covers a creator-focused marketplace with a shared order book. The NFT marketplace development guide covers marketplace types and costs in general.
Frequently asked questions
Is there an OpenSea clone script I can download?
OpenSea's website and backend are not open source, so no script copies them. Seaport, the settlement protocol, is open source, and you can build your own front end, indexer and order book on top of its contracts. Vendors who sell "OpenSea clone scripts" sell their own code, and that code needs the same review as any other software.
Do I need my own marketplace smart contract?
Usually not. The existing Seaport deployment lets your orders work on other venues, and you avoid auditing a new exchange. You may still deploy smaller contracts, such as a custom zone, a minting contract or a fee splitter.
How do royalties work on an OpenSea-style marketplace?
Your marketplace reads the royalty rate, for example through EIP-2981, and adds the payment to the order, but another marketplace can skip it. Only an NFT contract that limits transfers to approved operators, such as an ERC-721C contract, forces the payment.
Which chain should an OpenSea clone launch on?
Launch on the chain where your target collections and users already trade. Ethereum mainnet holds many high-value collections, while layer 2 networks such as Base, Arbitrum and Polygon offer cheaper trades.
Is running an open NFT marketplace legally risky?
Yes, it can be. Users may list infringing content or tokens that a regulator treats as securities, and card payments bring payment and anti-money-laundering duties. Get legal advice in your jurisdiction before launch, and write down a takedown process.