Ethereum is still where the most valuable NFT collections live and where NFT standards are defined. Building a marketplace for that ecosystem today usually means settling high-value trades on mainnet, deploying high-volume activity on an Ethereum Layer 2, and reusing proven order protocols rather than inventing your own.
Why Ethereum, and what changed
Ethereum's advantages for NFTs are mostly about trust and network effects: the deepest pool of collectors, the most audited contracts, broad wallet support, and the standards everyone else copies: ERC-721 for unique tokens, ERC-1155 for editions, and EIP-2981 for royalty information.
The platform has also changed substantially since the 2021 boom. Ethereum moved to proof of stake in September 2022, cutting its energy use dramatically. The Dencun upgrade in March 2024 introduced blob transactions (EIP-4844), which made Layer 2 transactions much cheaper. The Pectra upgrade in 2025 added EIP-7702, letting ordinary accounts use smart-account features such as batched transactions and sponsored gas. Mainnet fees fluctuate with demand, so do not hard-code fee assumptions into your business model.
Mainnet, Layer 2, or both?
| Choice | Good for | Watch out for |
|---|---|---|
| Ethereum mainnet | High-value art, blue-chip collections, collectors who want maximum security | Fees on every listing change, offer and trade; slow for games |
| Ethereum L2 (Base, Arbitrum, Optimism, ZKsync Era and others) | Open editions, gaming items, membership tokens, mainstream users | Liquidity is split across many L2s; bridging NFTs between them is awkward |
| Both | Marketplaces aggregating the whole Ethereum ecosystem | Multi-chain indexing, wallets and support |
Because L2s run the same EVM, the same contracts deploy to each with little change. The NFT Layer 2 guide compares the main rollups, and the ZKsync integration guide covers one where EVM differences matter.
Marketplace architecture
Order protocol
Modern Ethereum marketplaces use signed off-chain orders. A seller signs a typed message (EIP-712) describing what they offer and what they want in return; the order sits in your database at no gas cost; a buyer submits it to the exchange contract, which verifies the signature and swaps the assets atomically. OpenSea's open-source Seaport protocol is a widely used, heavily audited implementation that supports listings, collection offers, bundles and criteria-based offers. Many new marketplaces deploy on top of Seaport or integrate it rather than writing an exchange contract from scratch.
Royalties
EIP-2981 only tells marketplaces what royalty a creator wants; it cannot force payment. After the 2022 to 2023 "royalty wars", most major marketplaces made royalties optional or minimum-only for many collections. Creators who need enforcement use token-level approaches such as transfer validators (for example Limit Break's ERC-721C design), which restrict transfers to marketplaces that pay. Decide your policy explicitly and display it.
Off-chain services
- Indexer for collections, ownership and sales (a subgraph, an indexing framework, or a commercial NFT API).
- Order book database with signature validation, expiration and cancellation tracking.
- Metadata and media cache for IPFS and Arweave content.
- Fraud tooling: verified collections, stolen-item flags, and phishing-link detection.
Tooling in 2026
- Contracts: Solidity with OpenZeppelin libraries; Foundry or Hardhat for testing and deployment. The Solidity development guide covers the language side.
- Frontend: viem and wagmi (or ethers.js), with a wallet connection kit supporting injected, WalletConnect, and embedded wallets.
- Account abstraction: ERC-4337 smart accounts or EIP-7702 delegated accounts for gas sponsorship and one-click checkout.
- Storage: IPFS with reliable pinning, or Arweave for permanent storage.
Build steps
- Pick your niche and chain mix; a general-purpose OpenSea competitor is very hard to win, as the OpenSea comparison explains.
- Decide on the order protocol (integrate Seaport or build a custom exchange) and royalty policy.
- Build collection contracts or a launch tool for creators if you host primary sales.
- Build the indexer, order book, and metadata cache.
- Build the web app: browse, search, collection pages, listing, offers, checkout, profiles.
- Audit custom contracts, test on Sepolia, then deploy to mainnet or your chosen L2s.
Cost drivers
As a reasoned estimate, a niche marketplace built on Seaport with an indexer and polished frontend needs four to six engineers for three to five months. Writing your own exchange contract adds weeks and a larger audit. Ongoing costs are RPC and indexing, media storage, moderation, and gas if you sponsor transactions.
Frequently asked questions
Are Ethereum gas fees still too high for NFTs?
On mainnet they vary with demand and can still be significant for low-value items. On Layer 2s, typical transaction costs are a small fraction of mainnet, which is why most high-volume NFT activity has moved there.
Should I write my own marketplace contract?
Only if you need behavior that existing audited protocols cannot express. Seaport-based designs cover most listing and offer types and are trusted by wallets and aggregators.
Can my marketplace show NFTs from other marketplaces?
Yes. Because orders on Seaport-compatible venues are public, you can index and fill them. That is how aggregators work.