tokenIds

TokenID is a unique identifier assigned to a token within a system to distinguish it from other tokens and to link to its properties, owner, and state.

In blockchain token standards such as ERC-721 (NFTs) and ERC-1155, the TokenID is a non-negative integer that, together with the contract address, identifies a single token or token type. In ERC-721 each tokenId corresponds to an individual asset; the ownerOf(tokenId) function references it; tokenURI(tokenId) provides metadata. In ERC-1155 the tokenId identifies a token type, with balances held per account; multiple copies of the same tokenId may exist.

Token IDs can be generated in various formats, typically numeric uint256 in smart contracts, but sometimes UUIDs or hashed strings are used. The choice affects storage, indexing, and how metadata is associated.

Outside of blockchain, TokenIDs may reference digital licenses, vouchers, or access tokens in an API, or any system where distinct tokens represent rights or items; the ID is used to track issuance, revocation, and transfer.

Important considerations include ensuring global or contract-level uniqueness, immutability of the mapping, privacy concerns, and secure mapping to metadata; best practices include persisting authoritative sources, using canonical formats, and avoiding predictable sequences for sensitive systems.

See also: NFT, tokenization, digital asset, UUID.