Examine source code of everything you ever hearted.

{
  "manifest_version": 3,
  "name": "everything you ever hearted.",
  "version": "0.1.0",
  "description": "reads your library from Spotify. sends them to hearted. nothing else.",
  "permissions": [
    "storage",
    "cookies",
    "scripting"
  ],
  "host_permissions": [
    "https://*.spotify.com/*",
    "https://hearted.music/*",
    "https://*.hearted.music/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "hearted@hearted.music",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "authenticationInfo",
          "websiteContent"
        ]
      }
    }
  },
  "background": {
    "scripts": [
      "background/service-worker.js"
    ],
    "type": "module"
  },
  "content_scripts": [
    {
      "matches": [
        "https://open.spotify.com/*"
      ],
      "js": [
        "content/intercept-token.js"
      ],
      "world": "MAIN",
      "run_at": "document_start"
    },
    {
      "matches": [
        "https://open.spotify.com/*"
      ],
      "js": [
        "content/spotify-token.js"
      ],
      "run_at": "document_start"
    },
    {
      "matches": [
        "https://open.spotify.com/*"
      ],
      "js": [
        "content/return-banner.js"
      ],
      "run_at": "document_start"
    },
    {
      "matches": [
        "https://hearted.music/*",
        "https://*.hearted.music/*"
      ],
      "js": [
        "content/app-bridge.js"
      ],
      "run_at": "document_start"
    }
  ],
  "action": {
    "default_popup": "popup/index.html",
    "default_icon": {
      "16": "icons/icon-16.png",
      "48": "icons/icon-48.png",
      "128": "icons/icon-128.png"
    }
  },
  "icons": {
    "16": "icons/icon-16.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  }
}