OpenSea

OpenSea is a multi-chain NFT marketplace launched in 2017, providing a platform for users to discover, buy, sell, and manage non-fungible tokens across Ethereum, Polygon, Solana, and other supported networks. The marketplace supports ERC-721 and ERC-1155 token standards for Ethereum and EVM-compatible chains, covering digital art, collectibles, gaming assets, and domain names. OpenSea operates as a proprietary marketplace with select open-source protocol components — including the Seaport trading protocol and the OpenSea JS SDK — published under the ProjectOpenSea organization on GitHub

The marketplace is accessible at opensea.io without requiring users to hold a platform-specific token, as OpenSea does not have a native protocol token. Creators and collectors interact with the platform by connecting a supported Web3 wallet, which is used to sign transactions for listing items, placing offers, and completing purchases on-chain. OpenSea provides developer access through a REST API documented at docs.opensea.io and a TypeScript SDK through the OpenSea JS repository, enabling third-party applications to query NFT data and integrate marketplace functionality

The OpenSea marketplace interface allows users to browse NFT collections across supported chains, view item metadata, check listing histories, and inspect collection statistics such as floor price and trading volume. Individual NFT detail pages display the token's on-chain attributes, current listing status, offer history, and transfer history retrieved from the blockchain. The interface connects users' Web3 wallets for transaction signing — purchases, listings, and offers are submitted directly to the Seaport protocol or relevant chain contract rather than routed through a centralized backend for transaction execution

Sellers create listings for ERC-721 or ERC-1155 tokens at a fixed price or as a declining Dutch auction, with the listing recorded as a signed off-chain order that is fulfilled on-chain when a buyer accepts the terms. Buyers can submit offers — including collection-wide or trait-specific offers — which sellers can evaluate and accept through their connected wallet. This order book model, powered by the Seaport protocol on EVM chains, allows both fixed-price and offer-based trading without requiring a centralized escrow for assets during the listing period

OpenSea's multi-chain support aggregates NFT collections from Ethereum mainnet alongside Polygon, Solana, Arbitrum, Optimism, Base, and other supported networks into a single browsing interface, allowing users to discover and transact across different blockchain ecosystems without managing separate marketplace accounts per chain. Token standards covered include ERC-721 for unique one-of-one assets on EVM chains and ERC-1155 for multi-edition tokens with quantity, with Solana integration extending support to SPL NFT token programs. Cross-chain collection browsing is accessible from the same connected wallet interface, with the active chain context determined by the wallet's current network selection

Seaport is an open-source NFT trading protocol developed by ProjectOpenSea and available at github.com/ProjectOpenSea/seaport. The Seaport protocol handles on-chain order fulfillment logic for OpenSea trades on EVM-compatible networks — encoding offer and consideration terms into signed EIP-712 structured data that buyers and sellers exchange off-chain before on-chain settlement. The open-source nature of the Seaport protocol allows independent developers to inspect the contract logic, build marketplace applications on top of the protocol independently of the OpenSea interface, and integrate Seaport order fulfillment into custom applications

The OpenSea REST API, documented at docs.opensea.io/reference/api-overview, exposes endpoints for querying NFT metadata, collection statistics, listing data, offers, transfer history, and account information across supported chains. Developers access the API using keys obtained through the request process at docs.opensea.io/reference/request-an-api-key, enabling integration of OpenSea NFT data into external applications, analytics dashboards, portfolio trackers, and trading tools. The API provides a structured data retrieval layer on top of on-chain NFT state, covering both indexed metadata and current market data for supported collections

The OpenSea JS SDK, available as a TypeScript library at github.com/ProjectOpenSea/opensea-js, provides programmatic access to OpenSea marketplace functionality including listing creation, offer submission, and order fulfillment through the Seaport protocol. Developers building NFT marketplace applications or integrations can use the SDK to construct and execute Seaport orders without building raw contract interaction logic from scratch. The SDK wraps the Seaport protocol order structure and the OpenSea API data access into a unified TypeScript interface, reducing integration complexity for applications that need both data retrieval and transaction construction capabilities

OpenSea supports a range of NFT trading and discovery use cases across its supported networks: collectors browse and purchase NFTs from both established and emerging collections using the marketplace's search and filtering tools; creators list digital art, generative collections, and gaming assets for sale on Ethereum, Polygon, and other supported chains without building a custom storefront; traders place collection-wide or individual item offers to acquire NFTs at prices agreed upon with willing sellers; developers build NFT portfolio tools, analytics dashboards, and custom marketplaces using the OpenSea API and OpenSea JS SDK; and projects integrate Seaport protocol infrastructure to implement NFT trading mechanics within their own applications using the open-source contract as the underlying settlement layer

Developer integration with OpenSea is supported through the REST API documented at docs.opensea.io and the OpenSea JS SDK available on GitHub at github.com/ProjectOpenSea/opensea-js. The API provides read access to NFT metadata, collection data, listings, offers, and transfer records, with API keys requested through the documentation at docs.opensea.io/reference/request-an-api-key. The Seaport protocol repository at github.com/ProjectOpenSea/seaport contains the open-source smart contract code for the order fulfillment layer, providing a reference implementation for developers who want to understand the on-chain trading mechanics or integrate Seaport as an independent order protocol into their own marketplace applications

OpenSea operates as a proprietary marketplace platform, with centralized account protection, wallet approval monitoring, and listing integrity handled through the platform's own infrastructure. The Seaport trading protocol is open-source and independently auditable through the repository at github.com/ProjectOpenSea/seaport, allowing the on-chain order fulfillment logic to be reviewed by security researchers and developers independently of the marketplace. As a non-custodial marketplace, OpenSea does not hold user wallet keys or take custody of NFT assets outside of active Seaport order fulfillment transactions. Users should apply standard Web3 wallet security practices, including reviewing wallet approval requests before signing, and can consult the support center at support.opensea.io for guidance on account security and recognizing suspicious activity

OpenSea provides a multi-chain NFT marketplace covering collection discovery, fixed-price and offer-based trading, and browsing across Ethereum, Polygon, Solana, and other supported networks, with the open-source Seaport trading protocol handling on-chain order fulfillment. Developer access through the REST API and OpenSea JS SDK extends the platform's data and transaction capabilities to third-party applications, and the open-source Seaport repository provides an independently reviewable reference for the on-chain trading layer. Users and developers evaluating OpenSea should review the API documentation at docs.opensea.io, the Seaport repository at github.com/ProjectOpenSea/seaport, and the support center to understand available features, integration requirements, and platform policies across connected chains