結論

以下のブックマークレットを実行すると、その WordPress に登録されているユーザ情報が JSON で返ってきます。

javascript:(function(){location.href = location.protocol + "//" + location.host + "/wp-json/wp/v2/users"})()

実例

ヤマサ醤油株式会社のサイトを例にして、このブックマークレットを使ってみます。ヤマサ醤油株式会社のサイトは WordPress で作られています。

先ほどのブックマークレットを実行すると、以下のような JSON が返ってきます。これは単に REST API を叩いているだけです。

[{
  "id": 6,
  "name": "kasahara",
  "url": "",
  "description": "",
  "link": "https:\/\/www.yamasa.com\/author\/kasahara\/",
  "slug": "kasahara",
  "avatar_urls": {
    "24": "https:\/\/secure.gravatar.com\/avatar\/04af81b3f1bfeb542238dfe524a8fa23?s=24&d=mm&r=g",
    "48": "https:\/\/secure.gravatar.com\/avatar\/04af81b3f1bfeb542238dfe524a8fa23?s=48&d=mm&r=g",
    "96": "https:\/\/secure.gravatar.com\/avatar\/04af81b3f1bfeb542238dfe524a8fa23?s=96&d=mm&r=g"
  },
  "meta": [],
  "_links": {
    "self": [{
      "href": "https:\/\/www.yamasa.com\/wp-json\/wp\/v2\/users\/6"
    }],
    "collection": [{
      "href": "https:\/\/www.yamasa.com\/wp-json\/wp\/v2\/users"
    }]
  }
}, {
  "id": 13,
  "name": "ono",
  "url": "",
  "description": "",
  "link": "https:\/\/www.yamasa.com\/author\/ono\/",
  "slug": "ono",
  "avatar_urls": {
    "24": "https:\/\/secure.gravatar.com\/avatar\/002c6dcb31e30b024cca425e1e52ce05?s=24&d=mm&r=g",
    "48": "https:\/\/secure.gravatar.com\/avatar\/002c6dcb31e30b024cca425e1e52ce05?s=48&d=mm&r=g",
    "96": "https:\/\/secure.gravatar.com\/avatar\/002c6dcb31e30b024cca425e1e52ce05?s=96&d=mm&r=g"
  },
  "meta": [],
  "_links": {
    "self": [{
      "href": "https:\/\/www.yamasa.com\/wp-json\/wp\/v2\/users\/13"
    }],
    "collection": [{
      "href": "https:\/\/www.yamasa.com\/wp-json\/wp\/v2\/users"
    }]
  }
}, {
  "id": 8,
  "name": "recipe",
  "url": "",
  "description": "",
  "link": "https:\/\/www.yamasa.com\/author\/recipe\/",
  "slug": "recipe",
  "avatar_urls": {
    "24": "https:\/\/secure.gravatar.com\/avatar\/b565ca1b281f00abe81ccd542b9e2919?s=24&d=mm&r=g",
    "48": "https:\/\/secure.gravatar.com\/avatar\/b565ca1b281f00abe81ccd542b9e2919?s=48&d=mm&r=g",
    "96": "https:\/\/secure.gravatar.com\/avatar\/b565ca1b281f00abe81ccd542b9e2919?s=96&d=mm&r=g"
  },
  "meta": [],
  "_links": {
    "self": [{
      "href": "https:\/\/www.yamasa.com\/wp-json\/wp\/v2\/users\/8"
    }],
    "collection": [{
      "href": "https:\/\/www.yamasa.com\/wp-json\/wp\/v2\/users"
    }]
  }
}, {
  "id": 11,
  "name": "sam",
  "url": "",
  "description": "",
  "link": "https:\/\/www.yamasa.com\/author\/sam\/",
  "slug": "sam",
  "avatar_urls": {
    "24": "https:\/\/secure.gravatar.com\/avatar\/9648fbf81412fd2934f264543eba3677?s=24&d=mm&r=g",
    "48": "https:\/\/secure.gravatar.com\/avatar\/9648fbf81412fd2934f264543eba3677?s=48&d=mm&r=g",
    "96": "https:\/\/secure.gravatar.com\/avatar\/9648fbf81412fd2934f264543eba3677?s=96&d=mm&r=g"
  },
  "meta": [],
  "_links": {
    "self": [{
      "href": "https:\/\/www.yamasa.com\/wp-json\/wp\/v2\/users\/11"
    }],
    "collection": [{
      "href": "https:\/\/www.yamasa.com\/wp-json\/wp\/v2\/users"
    }]
  }
}, {
  "id": 1,
  "name": "\u682a\u5f0f\u4f1a\u793e\u30ef\u30fc\u30eb\u30c9\u30fb\u30ab\u30d5\u30a7",
  "url": "",
  "description": "",
  "link": "https:\/\/www.yamasa.com\/author\/worldcafe\/",
  "slug": "worldcafe",
  "avatar_urls": {
    "24": "https:\/\/secure.gravatar.com\/avatar\/30df7b0c4192b0cd804d284edf64db40?s=24&d=mm&r=g",
    "48": "https:\/\/secure.gravatar.com\/avatar\/30df7b0c4192b0cd804d284edf64db40?s=48&d=mm&r=g",
    "96": "https:\/\/secure.gravatar.com\/avatar\/30df7b0c4192b0cd804d284edf64db40?s=96&d=mm&r=g"
  },
  "meta": [],
  "_links": {
    "self": [{
      "href": "https:\/\/www.yamasa.com\/wp-json\/wp\/v2\/users\/1"
    }],
    "collection": [{
      "href": "https:\/\/www.yamasa.com\/wp-json\/wp\/v2\/users"
    }]
  }
}]