Metadata Preparation

LSP4 Metadata

When creating or editing Universal Profiles or Digital Assets, you will first need to upload assets such as images, icons, videos, etc. These assets can then be linked within the Metadata JSON File that will be attached to the smart contract.

This guide will walk you through all necessary steps to prepare the asset data.

Metadata Preparation Flow

To set the metadata of a digital asset, you have to follow these steps:

1. Upload each media file (icon, picture, image, video, etc) and get it's URLs or IPFS CID.
2. Inside the LSP4 Metadata JSON file , set the following values under each "images":
   • under verification.data, set the hash of the media file.
   • under url, set the value ipfs://<IPFS CID> (obtained from Step 1)
3. Upload the LSP4 Metadata JSON file to get its URL or IPFS CID.
4. Encode the LSP4 Metadata JSON file URL as a VerifiableURI.
5. Write the reference to the JSON file to your token contract.

1 - File Uploads

Storage Solution

LSPs do not restrict you to a specific storage solution.

To upload the files (assets and metadata JSON file), you have mainly two options:

Solution	Description	Examples
Centralized Storage	Centralized storage solutions are user-friendly and can be a good starting point for those new to the ecosystem or participating in hackathons. However, they rely on a single point of control, which may not align with the decentralized ethos of blockchain technology.	AWS S3, Google Cloud, Dropbox, etc.
Decentralized Storage	Decentralized storage solutions align with the decentralized nature of blockchain and offer benefits like redundancy, censorship resistance, and permanent storage. However, they might be more complex to interact with.	IPFS, Arweave, Filecoin, etc.

Uploading files to IPFS

See our guide "Use IPFS Storage" to learn how to upload your files to IPFS using the LUKSO tools-data-providers library.

2 - Generate the JSON File

The JSON content is used as input for encoding the metadata according to the LSP4 standard. After you filled your metadata file with content, upload it to a preferred storage solution.

To ensure the authenticity of the images, please generate the hash of the uploaded files and set them within the "verification" field of the JSON Metadata:

• Define the used hash function within the "method" element
• Add the hash digest (e.g: 32 bytes long for keccak256) within the "data" element

After uploading the media files, you can attach their links to a JSON File in the following structure:

LSP4 Example JSON File

{
    "LSP4Metadata": {
      "name": "My Token Name",
      "description": "Sample Description",
      "links": [{ "title": "My Website", "url": "https://my.website.com" }],
      "icon": [
        {
          "width": 60,
          "height": 60,
          "url": "https://mycentralised-storage.com/filename.png"
        }
      ],
      "images": [
        [
          {
            "width": 1000,
            "height": 1000,
            "url": "https://centralised-cloud-storage.com/image.jpg",
            "verification": {
              "method": "keccak256(bytes)",
              "data": "0x<hashOfTheUploadedFile>"
            }

          }
          {
            "width": 500,
            "height": 500,
            "url": "ipfs://[IPFS-CID]",
            "verification": {
              "method": "keccak256(bytes)",
              "data": "0x<hashOfTheUploadedFile>"
            }

          }
        ]
      ],
      "assets": [],
      "attributes": [
        {
          "key": "Standard type",
          "value": "LSP",
          "type": "string"
        },
        {
          "key": "Standard number",
          "value": 4,
          "type": "number"
        }
      ]
    }
  }

Prettified JSON

While the example above is formatted for readability, minifying the JSON file (removing whitespace and formatting) is recommended as it makes hash verification more consistent.

3 - Encode the LSP4 Metadata

Convenience Tool

You can use the 🛠️ erc725.js library to encode the LSP4 Metadata. The tool provides all necessary LSP schemas as well as the encodeData() function.

import { ERC725 } from '@erc725/erc725.js';
import LSP4DigitalAssetSchema from '@erc725/erc725.js/schemas/LSP4DigitalAsset.json';

const LSP4JSON = {
  /* Your JSON */
};

const encodedLSP4Metadata = ERC725.encodeData(
  {
    keyName: 'LSP4Metadata',
    value: {
      json: LSP4JSON,
      url: 'https://my-file-provider.com/my-file-link.json', // It can also be: ipfs://[CID]
    },
  },
  LSP4DigitalAssetSchema,
);

The encoded content will then look like the following:

LSP4 Encoded Contract Metadata

{
  keys: [
    '0x9afb95cacc9f95858ec44aa8c3b685511002e30ae54415823f406128b85b238e'
  ],
  values: [
    '0x00006f357c6a0020610be5a5ebf25a8323ed5a9d8735f78aaf97c7e3529da7249f17e1b4129636f3697066733a2f2f516d5154716865424c5a466e5155787535524473387441394a746b78665a714d42636d47643973756b587877526d'
  ]
}

4 - Adding the Metadata

After you retrieved the key and value of your ERC725Y data key, you can call the setData() function of the asset to update it's metadata on the contract.

Sample Implementation

You can follow our Deploy Token With Metadata and Set NFT Metadata Guides to set or update contract metadata.