Summary
The EIP-721 standard specification defining non-fungible tokens (NFTs) on the Ethereum blockchain. Establishes the interface (functions, events) that compliant smart contracts must implement to track and transfer unique digital assets. Distinguishes NFTs from fungible ERC-20 tokens by requiring per-token ownership tracking.
Key Points
- NFTs defined as individually distinct, non-interchangeable digital assets — each has a unique uint256 ID.
- Core functions:
ownerOf(),safeTransferFrom(),approve(),setApprovalForAll(). - Optional metadata extension: name, symbol, tokenURI — enables naming and describing each NFT.
- Optional enumeration extension: allows discovering all NFTs and those owned by an address.
- Scale: a contract deployed on testnet tracked 2^128 NFTs — scalability is not a structural limit.
- Design influenced by ERC-20 but fundamentally different: no
allowancefeature (quantity is always 0 or 1); transfer approval per-token or per-operator. - Early NFT examples: CryptoKitties, CryptoPunks, Decentraland LAND.
Newsletter Angles
- ERC-721 is the infrastructure layer that made the NFT boom (2021-2022) possible — a technical standard that created an explosion of speculative activity, like TCP/IP creating the dot-com era.
- The
tokenURIfunction points off-chain for metadata — meaning most NFTs are backed by a URL that can 404. The “ownership” is of a blockchain entry pointing to an image server, not the image itself. This is a structural fragility rarely discussed in NFT marketing. - “Deed” as the original intended term for NFT — implies the standard was conceived for property rights tracking, not speculative collectibles. The use cases diverged dramatically from the intent.
Concepts Mentioned
- Tokenomics — NFT tokenomics are a specialized case: supply per collection is fixed, but the NFT standard itself imposes no supply limit
Notes
Technical standard document. Authoritative source. The tokenURI off-chain metadata observation is not in the standard but is implied by the spec — implementations store metadata off-chain, creating the dependency.