BEP-721

BEP-721 is the technical standard for non-fungible tokens on BNB Smart Chain. It defines how a smart contract records unique tokens, each with its own identification number and owner, and how those tokens are transferred and approved for others to move. The standard is modelled closely on Ethereum's ERC-721, so the same functions, events and wallet behaviour apply, and existing Ethereum NFT code can be deployed on BNB Smart Chain with little change.

BEP stands for BNB Evolution Proposal, the process used to document standards and upgrades in the BNB Chain ecosystem. BEP-721 sits alongside the BEP-20 standard for fungible tokens and BEP-1155, which, like ERC-1155, lets one contract manage many token types at once. It has been used for game items, digital art, collectibles, membership passes and some tokenized certificates, particularly where users wanted lower fees than on Ethereum's main network.

Think of a cloakroom at a theatre. Each coat gets a numbered ticket, and no two tickets are the same. Whoever holds ticket 57 can collect the coat that goes with it, give the ticket to a friend, or ask the attendant to let someone else collect it on their behalf. The cloakroom keeps a list showing which ticket belongs to whom.

A BEP-721 contract is that cloakroom, running on BNB Smart Chain. Each token is a numbered ticket, the contract's list shows who owns it, and the ticket usually points to a description stored elsewhere, such as an image, a game character or a membership record. Because every cloakroom follows the same rules, any compatible wallet or marketplace knows how to read and move the tickets.

A BEP-721 contract implements a set of required functions and events:

• Ownership. A function returns the owner of a given token ID, and another returns how many tokens an address holds.
• Transfers. Owners can send a token to another address; a "safe" transfer checks that a receiving contract can handle NFTs, to avoid tokens getting stuck.
• Approvals. Owners can approve one address to move a single token, or approve an operator, such as a marketplace, to manage all their tokens.
• Events. Transfers and approvals emit events that wallets, explorers and marketplaces read to track ownership.
• Metadata. An optional extension gives each token a link, usually called a token URI, to a file describing its name, image and attributes.

Fees for minting and transferring are paid in BNB as gas. Token metadata is often stored off-chain, on a web server or on decentralized storage such as the InterPlanetary File System, because storing images on-chain is expensive.

BNB Smart Chain's low fees made BEP-721 popular for applications with many small transactions. Blockchain games used it for characters, land and equipment that players could trade; this area is described in NFTs in gaming. Collectible series and profile-picture projects, discussed under profile picture NFTs, issued tokens on the network, and NFT marketplaces, including Binance's own, supported BEP-721 assets. Some projects used the standard for event tickets, loyalty schemes and proof of attendance, and others for representing fractions or receipts in decentralized finance, for example liquidity positions in some exchanges. A broader overview appears in NFT use cases.

Because the two standards share the same interface, developers can usually reuse ERC-721 code, libraries and audits. The main differences come from the networks themselves. BNB Smart Chain has a smaller validator set and shorter block times than Ethereum, which lowers fees and speeds up confirmations but concentrates control among fewer operators. NFTs do not move automatically between the chains: an Ethereum NFT and a BNB Smart Chain NFT are separate tokens, and moving one requires a bridge that locks the original and issues a representation on the other network, introducing extra risk. Marketplaces and royalty arrangements also differ by network, so an NFT's liquidity depends heavily on where it was issued.

Owning a BEP-721 token proves control of an entry in a smart contract, not necessarily legal rights to the underlying artwork, game item or asset; those depend on the terms set by the issuer. If metadata is stored on a central server that goes offline, the token may point to nothing. Contracts can contain bugs or hidden functions that let the creator mint more tokens or block transfers, so audits and checks of the contract code matter. Fake collections that copy popular names are common, and phishing sites ask users to sign approvals that let attackers take all their NFTs, a risk covered in phishing. NFT trading volumes on BNB Smart Chain, as on other networks, have fallen sharply from their 2021 and 2022 peaks, and many collections have little or no market. As with any NFT, value depends on demand and is highly speculative.

• BNB Chain
• BNB Evolution Proposals on GitHub