ERC-721 is like the template for creating NFTs, those unique digital objects that don't repeat themselves. You can use it to make digital art, music, trading cards, video game characters, or anything you want that's special and different from the others. Each NFT has its own number and data, making it unique.

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ERC-721 is a proposed token standard for Ethereum and EVM-compatible networks that defines how to implement non-fungible tokens (NFTs): unique, indivisible and traceable digital assets. Unlike the ERC-20 standard, where all tokens are identical and fungible, in ERC-721 each token has a TokenID upscale, which makes it possible to represent unique assets with their own characteristics. This standard allows each token to be linked to a URI that points to its metadata, usually in JSON format, where the name, image, attributes and any relevant data are described. It is the technical base that has allowed the development and explosion of the NFT ecosystem, being adopted by digital art projects, music, virtual real estate, digital certificates, decentralized domains (such as ENS) or digital identities.

ERC-721 includes standard features such as OwnerOf (), transferFrom (), approve () and setApprovalForAll (), allowing for interoperability with marketplaces such as OpenSea or LooksRare. It also contemplates the logic of individual property, secure transfer, and authorization from third parties, making it a very solid framework for managing unique digital assets. Although its gas efficiency may be limited compared to ERC-1155 when managing multiple NFTs, its simplicity and standardization make it the preferred choice when it is necessary to represent assets in a completely individualized way.

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