Just a suggestion about a way to create OpenSea-style metadata for an ArtBlocks token.

exampleOutput.json

{
    "external_url": "https://api.artblocks.io/generator/18000234",
    "name": "MyProject by Me #234",
    "image": "https://api.artblocks.io/generator/18000234.jpg",
    "attributes": [{
        "trait_type": "serial_num",
        "value": 234,
        "max_value": 500,
        "display_type": "number"
    }, 
    {
        "trait_type": "series",
        "value": 18,
        "display_type": "number"
    }, 
    {
        "trait_type": "color_scheme",
        "value": "Grayscale"
    }, 
    {
        "trait_type": "chaos_factor",
        "value": 56,
        "max_value": 100
    }, 
    {
        "trait_type": "tile_shape",
        "value": 14,
        "max_value": 81
    }, 
    {
        "trait_type": "animation_speed",
        "value": 12,
        "max_value": 60
    }]
}

sketch.js

// Sample code for creating OpenSea-style metadata for an ArtBlocks token.
// Replace hardcoded params with real ones from the project.

let tokenData = {"hash":"0x31fa2d12d85e8aeea04e79dc9ed6d3fd2377de7d17fe4233e8c34aab4b48f0f6","tokenId":"18000234"};

function getMetadata(tokenData)
{
  let metadata = new TokenMetadata(tokenData, "MyProject by Me", "https://api.artblocks.io/generator/", 500);
  // 
  metadata.addTrait("color_scheme", "Grayscale");
  metadata.addTrait("chaos_factor", 56, 100);
  metadata.addTrait("tile_shape", 14, 81);
  metadata.addTrait("animation_speed", 12, 60);
  return metadata.getJson();
}

class TokenMetadata
{
  constructor(tokenData, projectName, uriPrefix, maxSupply = null, desc = null, bgColor = null)
  {
    this.tokenHash = tokenData.hash;
    this.tokenId = tokenData.tokenId;

    this.traits = [];

    this.tokenSerial = this.tokenId % 1000000;
    this.addTrait("serial_num", this.tokenSerial, maxSupply, "number");

    this.tokenSeries = Math.floor(this.tokenId / 1000000);
    this.addTrait("series", this.tokenSeries, null, "number");
    
    this.projectName = projectName;
    this.uriPrefix = uriPrefix;

    this.desc = desc;
    this.bgColor = bgColor;
  }

  addTrait(traitType, value, maxValue = null, displayType = null)
  {
    // trait_type is the name. Separate multi-word names with an underscore, 
    // like color_scheme, which will appear on OpenSea as "Color Scheme".
    // value can be a number or a string. If it's a string it always displays in the Properties section.
    let obj = {
      "trait_type": traitType,
      "value": value
    };
    // if you include max_value the attribute displays in the Levels section as a progress bar
    if (maxValue != null)
    {
      obj["max_value"] = maxValue;
    }
    // set display_type = "number" and it displays in the Stats section instead, like "1 of 250"
    if (displayType != null)
    {
      obj["display_type"] = displayType;
    }
    this.traits.push(obj);
  }

  getJson()
  {
    let obj = {
      "external_url": this.uriPrefix + this.tokenId,
      "name": this.projectName + " #" + this.tokenSerial,
      "image": this.uriPrefix + "images/" + this.tokenId + ".jpg", // or whatever
    }
    if (this.desc != null)
    {
      obj["description"] = this.desc;
    }
    if (this.bgColor != null)
    {
      obj["background_color"] = this.bgColor;
    }
    obj["attributes"] = this.traits;

    return JSON.stringify(obj);
  }
}