simple script to change wiki skin to monobook for Violentmonkey/tampermonkey/greasemonkey

Wmonobook.js

// ==UserScript==
// @name           change wiki skin to monobook
// Wikimedia projects
// @source         Zera's userscripts
// @include        *wikipedia.org*
// @include        *wiktionary.org*
// @include        *commons.wikimedia.org*
// @include        *wikiquote.org*
// @include        *wikibooks.org*
// @include        *wikisource.org*
// @include        *species.wikimedia.org*
// @include        *wikiversity.org*
// @include        *wikivoyage.org*
// @include        *wikifunctions.org*
// @include        *wikinews.org*
// Wikimedia
// @include        *meta.wikimedia.org*
// @include        **.wikimedia.org*
// @include        *mediawiki.org*
// Other
// @include        *wikiless.org*
// @include        *wiki.archlinux.org*
// @grant          none
// @run-at         document-start
// ==/UserScript==
// Other skins which are supported by wikipedia: timeless, minerva, vector, vector-2022 (by default)
// wikiless works fine only on vector

// store the current URL in a variable
url = location.href;
// remove "www." from the URL if it exists
url = url.replace(/^https?:\/\/www\./, "https://");
url = url.replace('?wprov=srpw1_0','');

// check if the URL includes "wikipedia.org", includes a "#" symbol, and does not include "&useskin=monobook"
if (url.includes("wikipedia.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  // find the index of the "#" symbol
  var hashIndex = url.indexOf("#");
  // make sure the hash value exists
  if (hashIndex !== -1) {
    // extract the hash value from the URL
    var hash = url.substring(hashIndex);
    // remove the hash value from the URL
    url = url.substring(0, hashIndex);
    // replace "wikipedia.org/wiki/" with "wikipedia.org/w/index.php?title="
    url = url.replace("wikipedia.org/wiki/", "wikipedia.org/w/index.php?title=");
    // append "&useskin=monobook" and the hash value to the URL
    url = url + "&useskin=monobook" + hash;
    // redirect the page to the updated URL
    location.href = url;
  }
}
// check if the URL includes "wikipedia.org" and does not include "&useskin=monobook"
else if (url.includes("wikipedia.org") && !url.includes("&useskin=monobook")) {
  // replace "wikipedia.org/wiki/" with "wikipedia.org/w/index.php?title="
  url = url.replace("wikipedia.org/wiki/", "wikipedia.org/w/index.php?title=");
  // append "&useskin=monobook" to the URL
  url = url + "&useskin=monobook";
  // redirect the page to the updated URL
  location.href = url;
}
if (url.includes("wiktionary.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("wiktionary.org/wiki/", "wiktionary.org/w/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes("wiktionary.org") && !url.includes("&useskin=monobook")) {
  url = url.replace("wiktionary.org/wiki/", "wiktionary.org/w/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}
if (url.includes("commons.wikimedia.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("commons.wikimedia.org/wiki/", "commons.wikimedia.org/w/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes("commons.wikimedia.org") && !url.includes("&useskin=monobook")) {
  url = url.replace("commons.wikimedia.org/wiki/", "commons.wikimedia.org/w/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}
if (url.includes("wikiquote.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("wikiquote.org/wiki/", "wikiquote.org/w/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes("wikiquote.org") && !url.includes("&useskin=monobook")) {
  url = url.replace("wikiquote.org/wiki/", "wikiquote.org/w/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}
if (url.includes("wikibooks.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("wikibooks.org/wiki/", "wikibooks.org/w/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes("wikibooks.org") && !url.includes("&useskin=monobook")) {
  url = url.replace("wikibooks.org/wiki/", "wikibooks.org/w/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}
if (url.includes("wikisource.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("wikisource.org/wiki/", "wikisource.org/w/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes("wikisource.org") && !url.includes("&useskin=monobook")) {
  url = url.replace("wikisource.org/wiki/", "wikisource.org/w/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}
if (url.includes("species.wikimedia.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("species.wikimedia.org/wiki/", "species.wikimedia.org/w/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes("species.wikimedia.org") && !url.includes("&useskin=monobook")) {
  url = url.replace("species.wikimedia.org/wiki/", "species.wikimedia.org/w/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}
if (url.includes("wikiversity.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("wikiversity.org/wiki/", "wikiversity.org/w/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes("wikiversity.org") && !url.includes("&useskin=monobook")) {
  url = url.replace("wikiversity.org/wiki/", "wikiversity.org/w/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}
if (url.includes("wikivoyage.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("wikivoyage.org/wiki/", "wikivoyage.org/w/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes("wikivoyage.org") && !url.includes("&useskin=monobook")) {
  url = url.replace("wikivoyage.org/wiki/", "wikivoyage.org/w/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}
if (url.includes("wikifunctions.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("wikifunctions.org/wiki/", "wikifunctions.org/w/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes("wikifunctions.org") && !url.includes("&useskin=monobook")) {
  url = url.replace("wikifunctions.org/wiki/", "wikifunctions.org/w/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}
if (url.includes("wikinews.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("wikinews.org/wiki/", "wikinews.org/w/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes("wikinews.org") && !url.includes("&useskin=monobook")) {
  url = url.replace("wikinews.org/wiki/", "wikinews.org/w/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}
if (url.includes("mediawiki.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("mediawiki.org/wiki/", "mediawiki.org/w/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes("mediawiki.org") && !url.includes("&useskin=monobook")) {
  url = url.replace("mediawiki.org/wiki/", "mediawiki.org/w/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}
if (url.includes(".wikimedia.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace(".wikimedia.org/wiki/", ".wikimedia.org/w/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes(".wikimedia.org") && !url.includes("&useskin=monobook")) {
  url = url.replace(".wikimedia.org/wiki/", ".wikimedia.org/w/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}
//wikiless
if (url.includes("wikiless.org") && url.includes("#") && !url.includes("&useskin=vector")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("wikiless.org/wiki/", "wikiless.org/w/index.php?title=");
    url = url + "&useskin=vector" + hash;
    location.href = url;
  }
}
else if (url.includes("wikiless.org") && !url.includes("&useskin=vector")) {
  url = url.replace("wikiless.org/wiki/", "wikiless.org/w/index.php?title=");
  url = url + "&useskin=vector";
  location.href = url;
}
//other
if (url.includes("wiki.archlinux.org") && url.includes("#") && !url.includes("&useskin=monobook")) {
  var hashIndex = url.indexOf("#");
  if (hashIndex !== -1) {
    var hash = url.substring(hashIndex);
    url = url.substring(0, hashIndex);
    url = url.replace("wiki.archlinux.org/title/", "wiki.archlinux.org/index.php?title=");
    url = url + "&useskin=monobook" + hash;
    location.href = url;
  }
}
else if (url.includes("wiki.archlinux.org") && !url.includes("&useskin=monobook")) {
  url = url.replace("wiki.archlinux.org/title/", "wiki.archlinux.org/index.php?title=");
  url = url + "&useskin=monobook";
  location.href = url;
}