An Ethereum NFT marketplace lists, sells and settles NFTs that follow Ethereum's token standards, on mainnet, on Ethereum layer 2 networks or on both. This guide explains the protocol upgrades that matter, the order and royalty design, the off-chain services, the tooling and the cost of a build.
Why build an NFT marketplace on Ethereum
The NFT standards that other chains copy started on Ethereum. ERC-721 defines unique tokens, ERC-1155 defines tokens with many copies, and EIP-2981 defines how a token reports its royalty. Wallets, indexers and audit firms all support these three standards, and many of the oldest and highest-priced collections also live on Ethereum mainnet.
Ethereum upgrades that affect NFT marketplaces
| Upgrade | Date | What changed for NFT apps |
|---|---|---|
| The Merge | September 2022 | Ethereum moved to proof of stake, which cut the network's energy use by more than 99%. |
| Dencun | March 13, 2024 | EIP-4844 added blobs, a cheap data space where rollups (layer 2 networks that post their data to Ethereum) store transaction data, which made layer 2 transactions much cheaper. |
| Pectra | May 7, 2025 | EIP-7702 lets a normal wallet account act like a smart account, which is a wallet controlled by contract code, so the account can bundle several actions into one transaction or let the app pay its gas. EIP-7691 raised blob capacity. |
| Fusaka | December 3, 2025 | With PeerDAS (peer data availability sampling), each node checks only samples of the blob data, so Ethereum can offer more blob space to rollups. |
The ethereum.org upgrade history lists Glamsterdam as the next upgrade, without a date. Mainnet fees change with demand, so a marketplace business plan should not assume a fixed fee level.
Mainnet, layer 2 or both
| Choice | Suits | Drawbacks |
|---|---|---|
| Ethereum mainnet | High-value art, established collections, collectors who want the strongest security | Every listing change, offer and trade costs gas, which is too slow and costly for games. |
| Ethereum layer 2 (Base, Arbitrum One, OP Mainnet, ZKsync Era and others) | Open editions, game items, membership tokens, mainstream users | Buyers and sellers are spread across many networks, and moving NFTs between layer 2 networks is awkward. |
| Both | Marketplaces that cover the whole Ethereum ecosystem | You must run indexing, wallet support and user support for several networks. |
Layer 2 networks run the same EVM, so the same contracts deploy to each with few changes. The layer 2 NFT guide compares the main rollups, and the ZKsync integration guide covers a rollup where EVM differences matter.
Ethereum NFT marketplace architecture
Order protocol
Most Ethereum marketplaces use signed orders that live off-chain until a trade happens:
- The seller signs a typed message in the EIP-712 format, stating what the seller offers and what the seller wants in return.
- The marketplace stores the signed order in its database, so listing costs the seller no gas.
- A buyer submits the order to the marketplace's exchange contract, an on-chain contract that settles trades.
- The exchange contract checks the signature and swaps the assets in one transaction.
OpenSea's open-source Seaport protocol handles listings, offers on whole collections, bundles of several NFTs, and offers on any token with traits the buyer names. Seaport 1.6 is the newest version listed in the Seaport repository, and it uses the same contract address on Ethereum, the main layer 2 networks and many other EVM chains. Trail of Bits audited Seaport in 2022, and many new marketplaces build on it or connect to it, so they do not need to write and audit their own exchange contract.
Royalties
EIP-2981 only reports the royalty a creator wants and cannot force a marketplace to pay it. During 2022 and 2023, most large marketplaces made royalties optional or set a low minimum for many collections.
Creators who want royalties enforced can restrict transfers at the token level. Limit Break's Creator Token Standards (ERC721-C) add a transfer validator that lets a collection block transfers through marketplaces that skip royalties. A marketplace should choose its royalty policy and show it on every collection page.
Off-chain services
- Indexer. Tracks collections, ownership and sales through a subgraph, an indexing framework or a commercial NFT API.
- Order book database. Checks signatures and tracks expiry and cancellation of each order.
- Metadata and media cache. Stores copies of IPFS and Arweave content.
- Fraud tools. Mark verified collections, flag stolen items and detect phishing links.
Tooling in 2026
- Contracts. Solidity with OpenZeppelin libraries, and Foundry or Hardhat for testing and deployment. The Solidity development guide covers the language.
- Frontend. viem and wagmi, or ethers.js, plus a wallet connection kit that supports browser wallets, WalletConnect and embedded wallets.
- Account abstraction. ERC-4337 smart accounts or EIP-7702 delegated accounts, for gas sponsorship and one-step checkout.
- Storage. IPFS with a paid pinning service, or Arweave for permanent storage.
Build steps
- Choose a niche and a chain mix, because a general marketplace competes with OpenSea directly, as the OpenSea comparison explains.
- Choose the order protocol, either Seaport or a custom exchange, and the royalty policy.
- Build collection contracts or a launch tool for creators, if the marketplace hosts primary sales.
- Build the indexer, the order book and the metadata cache.
- Build the web app: browsing, search, collection pages, listings, offers, checkout and profiles.
- Audit any custom contracts, test on the Sepolia testnet, then deploy to mainnet or the chosen layer 2 networks.
Team, timeline and cost drivers
The figures in this section are estimates, not quotes. A niche marketplace built on Seaport, with an indexer and a finished frontend, needs four to six engineers for three to five months, and a custom exchange contract adds several weeks and a larger audit.
Running costs cover RPC and indexing services, media storage, moderation, and gas if the marketplace pays fees for users.
Frequently asked questions
Are Ethereum gas fees still too high for NFTs?
Mainnet fees change with demand and can still be high for low-value items. On layer 2 networks, a typical transaction costs a small fraction of a mainnet transaction, which is why most high-volume NFT activity has moved there.
Should I write my own marketplace contract?
Write your own contract only if you need trade logic that audited protocols cannot express. Seaport covers most listing and offer types, and wallets and aggregators already support it.
Can my marketplace show NFTs listed on other marketplaces?
Yes. Orders on Seaport-based marketplaces are public, so your marketplace can index them and complete the trades for buyers, as aggregators do.
Which testnet should an Ethereum NFT marketplace use?
Sepolia is the main testnet for application testing, and Base, Arbitrum and OP Mainnet each run their own Sepolia-based testnets.