Github to GH Pages to Github Bookmarklet

ghregex.js

/*
  Takes you from a Github Repo URL to the GH Pages version on github.io
*/
javascript: (function() {
    var s = location.href;
    var r = /^((http[s]?|ftp):\/)?\/?([^:\/\s]+)((\/\w+)*\/)([\w\-\.]+[^#?\s]+)(.*)?(#[\w\-]+)?$/g;
    location.href = s.replace(r, "http:/$5.github.io/$6");
})();

// URL Encoded Version (for use as a bookmarklet)
javascript:(function()%7Bvar s%3Dlocation.href%3Bvar r%3D/%5E((http%5Bs%5D%3F%7Cftp):%5C/)%3F%5C/%3F(%5B%5E:%5C/%5Cs%5D%2B)((%5C/%5Cw%2B)*%5C/)(%5B%5Cw%5C-%5C.%5D%2B%5B%5E%23%3F%5Cs%5D%2B)(.*)%3F(%23%5B%5Cw%5C-%5D%2B)%3F%24/g%3Blocation.href%3Ds.replace(r,"http:/%245.github.io/%246")%3B%7D)()%3B

/*
  Takes you from a GH Pages URL to the Github Repo
*/
javascript: (function() {
    var s = location.href;
    var r = /^((http[s]?|ftp):\/)?\/?([^:\.\s]+).([^:\.\s]+).([^:\/\s]+)((\/\w+)*\/)([\w\-\.]+[^#?\s]+)(.*)?(#[\w\-]+)?$/g;
    location.href = s.replace(r, "http://github.com/$3/$8");
})();

// URL Encoded Version (for use as a bookmarklet)
javascript:(function()%7Bvar%20s%20%3D%20location.href%3Bvar%20r%20%3D%20%2F%5E((http%5Bs%5D%3F%7Cftp)%3A%5C%2F)%3F%5C%2F%3F(%5B%5E%3A%5C.%5Cs%5D%2B).(%5B%5E%3A%5C.%5Cs%5D%2B).(%5B%5E%3A%5C%2F%5Cs%5D%2B)((%5C%2F%5Cw%2B)*%5C%2F)(%5B%5Cw%5C-%5C.%5D%2B%5B%5E%23%3F%5Cs%5D%2B)(.*)%3F(%23%5B%5Cw%5C-%5D%2B)%3F%24%2Fg%3Blocation.href%20%3D%20s.replace(r,"http://github.com/$3/$8")%3B%7D)()%3B

Noice.

Here is a combo that works both ways so you don't need 2 bookmarklet

javascript:location = location.href.replace(...[...location.host === "github.com" 
  ? [/^((http[s]?):\/)?\/?([^:\/\s]+)((\/\w+)*\/)([\w\-\.]+[^#?\s]+)(.*)?(#[\w\-]+)?$/g, "https:/$5.github.io/$6"]
  : [/^((http[s]?):\/)?\/?([^:\.\s]+).([^:\.\s]+).([^:\/\s]+)((\/\w+)*\/)([\w\-\.]+[^#?\s]+)(.*)?(#[\w\-]+)?$/g, "https://github.com/$3/$8"]])