ERC-6785: ERC-721 Utilities Information Extension

Provide easy access to information about the `utility` of an NFT via functions and the NFT's metadata

Abstract

This specification defines standard functions and an extension of the metadata schema that outlines what a token’s utility entails and how the utility may be used and/or accessed. This specification is an optional extension of ERC-721.

Motivation

This specification aims to clarify what the utility associated with an NFT is and how to access this utility. Relying on third-party platforms to obtain information regarding the utility of the NFT that one owns can lead to scams, phishing or other forms of fraud.

Currently, utilities that are offered with NFTs are not captured on-chain. We want the utility of an NFT to be part of the metadata of an NFT. The metadata information would include: a) type of utility, b) description of utility, c) frequency and duration of utility, and d) expiration of utility. This will provide transparency as to the utility terms, and greater accountability on the creator to honor these utilities.

As the instructions on how to access a given utility may change over time, there should be a historical record of these changes for transparency.

Specification

The keywords “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.

Every contract compliant with ERC-6785 MUST implement the interface defined as follows:

Contract Interface

// @title NFT Utility description
///  Note: the EIP-165 identifier for this interface is ed231d73

interface IERC6785 {

    // Logged when the utility description URL of an NFT is changed
    /// @notice Emitted when the utilityURL of an NFT is changed
    /// The empty string for `utilityUri` indicates that there is no utility associated
    event UpdateUtility(uint256 indexed tokenId, string utilityUri);

    /// @notice set the new utilityUri - remember the date it was set on
    /// @dev The empty string indicates there is no utility
    /// Throws if `tokenId` is not valid NFT
    /// @param utilityUri  The new utility description of the NFT
    /// 4a048176
    function setUtilityUri(uint256 tokenId, string utilityUri) external;

    /// @notice Get the utilityUri of an NFT
    /// @dev The empty string for `utilityUri` indicates that there is no utility associated
    /// @param tokenId The NFT to get the user address for
    /// @return The utility uri for this NFT
    /// 5e470cbc
    function utilityUriOf(uint256 tokenId) external view returns (string memory);

    /// @notice Get the changes made to utilityUri
    /// @param tokenId The NFT to get the user address for
    /// @return The history of changes to `utilityUri` for this NFT
    /// f96090b9
    function utilityHistoryOf(uint256 tokenId) external view returns (string[] memory);
}

All functions defined as view MAY be implemented as pure or view

Function setUtilityUri MAY be implemented as public or external. Also, the ability to set the utilityUri SHOULD be restricted to the one who’s offering the utility, whether that’s the NFT creator or someone else.

The event UpdateUtility MUST be emitted when the setUtilityUri function is called or any other time that the utility of the token is changed, like in batch updates.

The method utilityHistoryOf MUST reflect all changes made to the utilityUri of a tokenId, whether that’s done through setUtilityUri or by any other means, such as bulk updates

The supportsInterface method MUST return true when called with ed231d73

The original metadata SHOULD conform to the “ERC-6785 Metadata with utilities JSON Schema” which is a compatible extension of the “ERC-721 Metadata JSON Schema” defined in ERC-721.

“ERC-6785 Metadata with utilities JSON Schema” :

{
  "title": "Asset Metadata",
  "type": "object",
  "properties": {
    "name": {
      "type": "string",
      "description": "Identifies the asset to which this NFT represents"
    },
    "description": {
      "type": "string",
      "description": "Describes the asset to which this NFT represents"
    },
    "image": {
      "type": "string",
      "description": "A URI pointing to a resource with mime type image/* representing the asset to which this NFT represents. Consider making any images at a width between 320 and 1080 pixels and aspect ratio between 1.91:1 and 4:5 inclusive."
    },
    "utilities": {
      "type": "object",
      "required": [
        "type",
        "description",
        "t&c"
      ],
      "properties": {
        "type": {
          "type": "string",
          "description": "Describes what type of utility this is"
        },
        "description": {
          "type": "string",
          "description": "A brief description of the utility"
        },
        "properties": {
          "type": "array",
          "description": "An array of possible properties describing the utility, defined as key-value pairs",
          "items": {
            "type": "object"
          }
        },
        "expiry": {
          "type": "number",
          "description": "The period of time for the validity of the utility, since the minting of the NFT. Expressed in seconds"
        },
        "t&c": {
          "type": "string",
          "description": ""
        }
      }
    }
  }
}

Rationale

Since the utilityUri could contain information that has to be restricted to some level and could be dependent on an off-chain tool for displaying said information, the creator needs the ability to modify it in the event the off-chain tool or platform becomes unavailable or inaccessible.

For transparency purposes, having a utilityHistoryOf method will make it clear how the utilityUri has changed over time.

For example, if a creator sells an NFT that gives holders a right to a video call with the creator, the metadata for this utility NFT would read as follows:

{
  "name": "...",
  "description": "...",
  "image": "...",
  "utilities": {
    "type": "Video call",
    "description": "I will enter a private video call with whoever owns the NFT",
    "properties": [
      {
        "sessions": 2
      },
      {
        "duration": 30
      },
      {
        "time_unit": "minutes"
      }
    ],
    "expiry": 1.577e+7,
    "t&c": "https://...."
  }
}

In order to get access to the details needed to enter the video call, the owner would access the URI returned by the getUtilityUri method for the NFT that they own. Additionally, access to the details could be conditioned by the authentication with the wallet that owns the NFT.

The current status of the utility would also be included in the URI (eg: how many sessions are still available, etc.)

Backwards Compatibility

This standard is compatible with current ERC-721 standard. There are no other standards that define similar methods for NFTs and the method names are not used by other ERC-721 related standards.

Test Cases

Test cases are available here

Reference Implementation

The reference implementation can be found here.

Security Considerations

There are no security considerations related directly to the implementation of this standard.

Copyright

Copyright and related rights waived via CC0-1.0.

Citation

Please cite this document as:

Otniel Nicola (@OT-kthd), Bogdan Popa (@BogdanKTHD), "ERC-6785: ERC-721 Utilities Information Extension [DRAFT]," Ethereum Improvement Proposals, no. 6785, March 2023. [Online serial]. Available: https://eips.ethereum.org/EIPS/eip-6785.