ERC-721 is the Ethereum standard for non-fungible tokens — assets that are individually distinguishable rather than interchangeable. It defines ownership, transfer and approval for unique token IDs, and a metadata extension pointing at the content a token represents.
ERC-721
ERC-721 did for unique assets what ERC-20 did for fungible ones: a common interface, so a wallet or marketplace can display and move an item it has never seen. The metadata extension — a URI per token — is where the asset’s actual content lives, and where most of the durability questions sit.
- Per-token identity - Ownership tracked by token ID rather than by balance.
- Approvals per token or per operator - Delegation at two granularities, both worth understanding before signing one.
- A metadata URI - The token points at its content; whether that pointer survives is a property of where it points.
- Marketplace interoperability - Any conforming marketplace can list any conforming token.
The consumer end of this market is also its weakest published surface: The State of Blockchain & Crypto APIs scores NFT, gaming and consumer web3 at 20.5 with 29.3% publishing a machine-readable contract — the widest gap between public attention and published evidence in the catalog, in the segment built directly on this standard.
