Overview
Definition
Metadata provides information that is not directly used for a contract's operation. It describes the contract's code or the off-chain meaning of its contents.
Metadata are standardized through the TZIP system.
They are two types of metadata:
| Name | Specification | Description |
|---|---|---|
| Contract metadata | TZIP-16 (TZIP-12 for FA2) | Describe the whole contract (e.g. interface, versioning) and the off-chain views. |
| Token metadata | TZIP-16, TZIP-12 and TZIP-21 | Used in the FA2 standard. They describe one token (e.g. an artwork corresponding to an NFT). |
Usage
The usage of metadata is very large.
Metadata are used by contracts explorers to show additional information about the contracts: a name, an author, the source code... and additional features: off-chain views. Off-chain views let people get more structured info from the the contract without having to send a transaction nor use a wallet. They can simplify decentralized applications job by abstracting the contract's storage.
Metadata are used by platforms like NFT marketplaces to list NFTs and collections. They are used by wallets to show tokens and improve feedbacks when interacting (by printing more explicit errors for example).
These usages are really open and you can invent your own like adding a link to a CSV file or to real world geo-coordinates to a contract.