ERC-721
Padrão técnico para criar tokens não fungíveis na Ethereum, em que cada unidade é única e não intercambiável, com identidade própria registrada.
Key points
- ERC-721 is the technical standard for creating non-fungible tokens on networks compatible with the Ethereum Virtual Machine.
- Unlike ERC-20, where every unit is identical, in ERC-721 each token has its own identifier and is unique.
- It is the format behind most NFTs, used to represent collectibles, tickets, and other individual assets.
What is ERC-721?
ERC-721 is the specification that defines how to create non-fungible tokens, or NFTs, on Ethereum-compatible networks. While ERC-20 deals with interchangeable assets, ERC-721 deals with unique items: each token carries an identifier that distinguishes it from every other token in the same contract. This uniqueness is what makes it possible to register ownership of something specific on the blockchain.
How it works
An ERC-721 contract manages a collection of tokens, each with a unique identifier and a registered owner. The standard defines functions to transfer ownership of a specific token, query who owns each identifier, and authorize third parties to move it. Because each unit is unique, operations always refer to an individual token rather than a quantity.
Generally, each token points to metadata describing what it represents, such as an item's name and image. This metadata and its associated content are often stored off-chain for cost reasons, while the contract records ownership and the authenticity of the reference on the blockchain.
Standardization allows wallets and marketplaces to display and trade any NFT in the ERC-721 format, in the same way ERC-20 standardized fungible tokens.
Why it matters
ERC-721 gave the ecosystem a standardized way to register ownership of unique items on-chain. For businesses, the practical interest usually lies in using this format to represent receipts, tickets, and verifiable rights in an auditable way, more than in speculating on collectibles.
Limitations
If the content referenced by a token is hosted off-chain and disappears, the NFT may end up pointing to nothing, undermining what it represents. Owning the token also does not always equate to legal rights over the item. And, like any contract, a poorly built implementation can contain flaws that affect holders. For this reason, assessing where the metadata is hosted is part of judging the durability of an NFT.