What Is ERC-721?
ERC-721 is the Ethereum standard for non-fungible tokens. Each token has an ID. ID 47 is not interchangeable with ID 48. That is what lets a CryptoPunk or a Fidenza be "this one" instead of "a unit of." NFT marketplaces speak 721 (and sometimes 1155) the way DEXs speak ERC-20.
How It Actually Works
- The contract maps token IDs to owners and usually points at metadata: a name, a link to an image. The image is often not on Ethereum. The pointer is.
- Transfers move the ID. Approvals can let a marketplace move it for you. Same permission danger as fungible tokens, different asset.
- The standard does not lock royalties, keep the art online, or force the team to keep building. When they leave, you still own the ID. See when a project disappears.
Risks and Common Mistakes
- Buying a 721 that copies a famous collection. Verify the contract against the project's own site, not the search bar.
- Signing a marketplace offer you did not mean to sign. Read the wallet prompt. OpenSea and Tensor are venues, not babysitters.
When It Matters
Any Ethereum NFT, and any time someone says "it's on-chain" without saying whether they mean the token, the picture, or the vibe.
Related Terms
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