thumbnail

Allows you to add thumbnail to the embed. Currently, there is no way to set width/height of the thumbnail. url value must be valid url that starts with http(s):// or attachment://, more info about the latter one can be found on the file page.

Example:

{
  "embeds": [{
    "thumbnail": {
      "url": "https://upload.wikimedia.org/wikipedia/commons/3/38/4-Nature-Wallpapers-2014-1_ukaavUI.jpg"
    }
  }]
}