ERC-721

What is ERC-721?

ERC-721 is the original Ethereum standard for non-fungible tokens (NFTs). It provides a set of rules that allow for the creation of unique, individual tokens on the blockchain that cannot be exchanged one-for-one.

How does ERC-721 work?

1. Every ERC-721 token has a unique uint256 ID within its contract.
2. The contract maintains a mapping that links each token ID to a specific owner's address.
3. It includes functions to transfer ownership and approve third parties to move tokens.
4. The standard allows for "metadata" (like a name or image link) to be associated with each ID.
5. Because it is a standard, any wallet or marketplace can interact with any ERC-721 token without custom code.

Why does ERC-721 matter?

ERC-721 enabled the "digital ownership" revolution. It made it possible to prove the rarity and authenticity of digital art, collectibles, and even real estate.

Key features of ERC-721

• Unique token IDs (non-fungible)
• Publicly verifiable ownership
• Permissionless trading and transfers
• Metadata support for external assets
• Foundation of the NFT ecosystem

Examples of ERC-721

The Bored Ape Yacht Club (BAYC) and CryptoPunks are famous examples of ERC-721 collections. Every Ape and Punk is a unique token with its own ID and specific owner on the Ethereum blockchain.