tokenuri

TokenURI, commonly written tokenURI, refers to a function in NFT smart contracts that returns a URI pointing to a JSON metadata document for a given token ID. In the ERC-721 standard, tokenURI(uint256 tokenId) is part of the metadata extension and must return a string representing the location of the token’s metadata. The metadata document is typically a JSON object containing fields such as name, description, image, and attributes. The image field is usually a URL or an IPFS link to the media asset; attributes is an array of trait objects used for showcasing token characteristics.

The URI may use various schemes, including https, ipfs, or data URIs. When metadata is hosted off-chain, the URI serves as a pointer to the data, allowing metadata to be updated independently of the contract. To improve decentralization and immutability, many projects store metadata on IPFS or other decentralized storage. ERC-1155 uses a different approach: a base URI with a placeholder {id} that can be replaced by the token’s ID.

Implementations may build tokenURI by concatenating a baseURI with the tokenId or by returning a full URI stored per token. Some marketplaces read tokenURI to fetch metadata and render NFT details. The specificity of tokenURI is not enforced beyond returning a string; the format of the metadata is defined by the project.

See also: ERC-721, ERC-1155, metadata extension.