Ledger LandISSUE #37 of 90

erc-721 · the nft standard

BlockyVSDouble-Spend Dan

Blocky saysERC-721 is the standard for NFTs — each token is unique and non-interchangeable.

Where ERC-20 tokens are identical, ERC-721 non-fungible tokens each have a unique tokenId and owner. The interface tracks ownership and transfers per id, and typically points at off-chain metadata (image, traits) via a URI. It's the basis of digital art, collectibles, in-game items, and any "this specific thing belongs to this address" use case.

Power-ups you unlock

Non-fungible: each tokenId is unique
Tracks per-id ownership and transfer
Metadata (image/traits) usually off-chain via URI
Art, collectibles, game items, deeds

Double-Spend Dan attacks — common mistakes

Storing large media on-chain (too costly)
Assuming the image is on-chain (usually a URI)
Confusing ERC-721 with ERC-20 semantics

Boss battleExplain why an NFT’s artwork usually isn’t stored on-chain.

Example code

<!doctype html><html><head><meta charset="utf-8"></head>
<body style="background:#06040d;color:#e6e0ff;font-family:monospace;padding:20px"><pre>ERC-721: ownerOf(tokenId), transferFrom
tokenId 7 → owner 0xabc… → tokenURI → metadata/image
each token unique</pre></body></html>

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