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An NFT smart contract is blockchain program code that applies token rules and keeps track of tokens and their state. It is not the artwork or other item associated with an NFT. On Ethereum, an NFT is identified by its contract address and token ID; metadata and media may be stored elsewhere and referenced by the contract.
What an NFT smart contract is—and what it is not
A smart contract is a program deployed on a blockchain. An NFT smart contract defines how tokens are created and handled, and records information such as which address owns a token. The NFT is an individual token managed by that program. The associated image, game item, or other content is a separate asset, not the contract itself.
Ethereum’s ERC-721 specification describes its standard as “A standard interface for non-fungible tokens, also known as deeds.” ERC-721 standardizes key ways applications can query and manage these tokens; it does not require every project to have identical creation rules or additional behavior. Read the ERC-721 specification.
How an Ethereum NFT contract works
- Minting: A creator or other authorized caller invokes contract functionality to create a token and assign it to an address. Who is allowed to mint depends on the contract’s implementation.
- Ownership queries: ERC-721 defines functions such as
ownerOf, which returns the owner of a specified token, andbalanceOf, which reports an address’s token balance. - Transfers and approvals: Owners can transfer tokens using standard functions such as
transferFromorsafeTransferFrom. Approval functions can authorize an address for a specific token or an operator for an owner’s tokens. A safe transfer checks whether a receiving contract can accept the token. - Recorded changes: ERC-721’s
Transferevent reports transfers and, under the standard’s rules, minting and burning. Wallets and other applications can use contract data and events to display token ownership and activity.
ERC-721-compliant contracts implement the required ERC-721 and ERC-165 interfaces, subject to the specification’s caveats. Projects can add behavior and implementation-specific restrictions, so the standard interface alone does not tell you every rule in a particular collection. Ethereum.org explains ERC-721.
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How to identify a specific NFT
Under ERC-721, a token ID is unique within its contract. The contract address plus that token ID identifies a specific NFT on Ethereum. A token ID by itself is not enough to identify the token globally, because different contracts can use the same ID. Ethereum.org’s NFT overview explains how tokens and their identifiers fit into the broader NFT model.
Where an NFT’s metadata and media are stored
The token record and the NFT’s descriptive information are distinct. ERC-721’s metadata extension is optional; where implemented, tokenURI returns a URI for the token’s metadata. That URI may point to a JSON document containing fields such as a name, description, and image. The standard does not require the image or complete metadata document to be stored inside the contract. The ERC-721 specification defines the optional metadata interface and gives an example schema.
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As a result, seeing an NFT in a wallet does not mean its full media file is embedded in the token contract. The contract manages token behavior and state; metadata and media are referenced separately.
ERC-721 vs. ERC-1155
ERC-721 is designed around individually identified NFTs. ERC-1155 is a multi-token standard: one contract can manage multiple token types, including fungible, non-fungible, and semi-fungible configurations. It also supports batch operations, which can be useful when a project handles several items or transfers together. A token type with a supply of one is essentially an NFT.
| Feature | ERC-721 | ERC-1155 |
|---|---|---|
| What one contract manages | Individually identified non-fungible tokens | Multiple token types, which can be fungible, non-fungible, or semi-fungible |
| Batch operations | Not the defining capability described by the standard | Supports batch operations |
| Typical fit | Projects centered on individually tracked NFTs | Projects that need several token types or batch transfers |
The standards have different interfaces and are not interchangeable in every detail. Check which standard a particular contract uses rather than assuming every NFT follows ERC-721. The ERC-1155 specification defines the multi-token standard.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What NFT ownership does not establish
A contract can record that an address owns a token, but that technical record alone does not establish that the owner has copyright or legal title to the associated work. Those rights depend on the applicable terms and law, not simply on the token standard.
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