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chip-0007.md

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CHIP Number 0007
Title Off-chain metadata format for NFT1
Description A standard for formatting off-chain metadata for NFT1-compliant NFTs on Chia's blockchain
Author Will Riches
Editor Dan Perry
Comments-URI Chia-Network#26
Status Final
Category Process
Sub-Category Other
Created 2022-06-25
Requires 0005
Replaces None
Superseded-By None

Abstract

The Chia NFT1 standard enables an off-chain metadata file to be referenced by Non-Fungible Tokens (NFTs) on chain, along with a hash of the file that ensures its immutability. This CHIP describes a standard format for off-chain metadata files. It is intended to be used with image-based NFTs but could be used with other types of media.

Motivation

The NFT1 standard does not require compliant NFTs to reference an off-chain metadata file. If an off-chain metadata file is used, it is not required to be in any particular file format or conform to a particular data model or schema.

For projects in the Chia ecosystem to be able to create, display and interact with NFTs in a consistent manner, some coordination of metadata file formats is necessary.

Backwards Compatibility

If this CHIP is accepted and the data format becomes widely used by projects in the Chia NFT ecosystem, it is possible that non-compliant NFTs which have already been minted will not be displayed correctly, or at least may not have their full metadata displayed. However, the same risk is present without this CHIP being put forward, since there would be little standardization.

Rationale

  • For wide compatibility with developers, JSON format was selected.
  • To avoid low quality data being used unnecessarily, only a minimal set of fields are required to be compliant with the format.
  • A collection object is included, which would result in collection information being duplicated across each NFT in the collection. Although storage is not a large problem since the metadata is off chain, this data structure is not ideal since NFT tools will have to parse collection information from each NFT and potentially deal with mismatches. However, this is seen as an acceptable interim measure until collection information is directly referenced on chain.
  • Collection data is optional, but if it is included it must include both a collection id and name to enable collections to be grouped more easily.

Specification

The metadata file must be in JSON format. Typically, the metadata file will have a .json extension, but this is not required.

In this section, the schema of the root JSON object is described.

Properties

Property Type Required Description
format string Yes CHIP number of the metadata format Possible values are: CHIP-0007.
name string Yes Name of the NFT
description string Yes Description of the NFT
minting_tool string No Name or short tag of the minting tool used to create this NFT
sensitive_content boolean or string[] No Indicator for sensitive content within the NFT
series_number integer No Number that this NFT is within the series (sequence of distinct NFTs)
series_total integer No Total number of NFTs within the series (sequence of distinct NFTs)
attributes object[] No Attributes of the NFT that may be directly displayed to the user
collection object No NFT collection information
data [object] No Any NFT data which is not suitable for the atrtributes array, such as non-human-readable data

attributes

Attributes of the NFT that may be directly displayed to the user

Properties

Property Type Required Description
trait_type integer or string Yes Name of the NFT attribute
value integer or string Yes Value of the NFT attribute
min_value integer No Minimum value of the NFT attribute in relation to other NFTs. Only applicable to integers.
max_value integer No Maximum value of the NFT attribute in relation to other NFTs. Only applicable to integers.

collection

NFT collection information

Properties

Property Type Required Description
id string Yes ID of the NFT collection
name string Yes Name of the NFT collection
attributes object[] No Attributes of the NFT collection
  • See errata regarding a missing property from this table

attributes

Attributes of the NFT collection

Properties
Property Type Required Description
type integer or string Yes Name of the NFT collection attribute
value integer or string Yes Value of the NFT collection attribute

Reference Implementation

The schema is made available for consumption as a JSON Schema dialect. The dialect can be used to validate that metadata files are compliant with the schema.

An example metadata file has also been included.

Security

Currently, there are no requirements of the metadata's file format or data structure. From a security perspective, introducing a standard format is only a net gain.

This format includes collection information, which itself does not verify the legitimacy of the collection. It is incumbent on NFT tools and services to combine this collection information with verifiable ownership data, such as the DID of the creator. The risk of NFT tools not implementing these checks is not introduced by this format, but it's possible that the availability of collection information in a standard metadata format could infer that this information is verified. This can be prevented by providing clear information and documentation to developers.

Additional Assets

Errata

  • The JSON schema associated with this CHIP correctly states that a collection's ID is required to be a String in uuid format. However, the specific format is missing from the specification laid out in this document. Despite this omission, the format for the id property of a collection is required to be uuid
  • The JSON schema associated with this CHIP correctly states that the series_number and series_total properties are required to be integers with a minimum value of 1. However, these specific values are missing from the specification laid out in this document. Despite this omission, the minimum value for the series_number and series_total properties is 1.

Copyright

Copyright and related rights waived via CC0.