Broken Link OR Dead link (404 Error)

A dead link (also called a broken link or dangling link) is a link on the World Wide Web that points to a web page or server that is permanently unavailable. The most common result of a dead link is a 404 error, which indicates that the web server responded, but the specific page could not be found. The browser may also return a DNS error indicating that a web server could not be found at that domain name. A link might also be dead because of some form of blocking such as content filters or firewalls.

Another type of dead link is a URL that points to a site unrelated to the content sought. This can sometimes occur when a domain name is allowed to lapse, and is subsequently reregistered by another party. Domain names acquired in this manner are attractive to those who wish to take advantage of the stream of unsuspecting surfers that will inflate hit counters and PageRanking.

Link rot is the process by which links on a website gradually become irrelevant or broken over time as sites they link to disappear, change content, or redirect to new locations.

Links specially crafted to not resolve, as a type of meme, are known as Zangelding, which roughly translated from German means tangle thing. A zangelding is basically a list of self referencing broken links.

Dead links commonplace on the Internet can also occur on the authoring side, when website content is assembled, copied, or deployed without properly verifying the targets, or simply not kept up to date. Because broken links are to some very annoying, generally disruptive to the user experience, and can live on for many years, sites containing them are regarded as unprofessional.

Solutions to broken links:

Due to the unprofessional image that dead links bring to both sites linking and linked to, there are multiple solutions that are available to tackle them - some working to prevent them in the first place, and others trying to resolve then when they have occurred.

* The most obvious form of link management, is employing link checking software that test each link on a website for its validity. An example of, and one of the most widely used link checkers is Xenu's Link Sleuth.
* Content Managment Systems often offer inbuilt solutions to the management of links, eg. links are updated when content is changed or moved on the site.
* Permalinking stops broken links by guaranteeing that the content will never move. Another form of permalinking is linking to a permalink that then redirects to the actual content, ensuring that even though the real content may be moved etc..., links pointing to the resources stay intact.
* The Wayback Machine, operated by the Internet Archive, keeps historical snapshots of websites. If a dead link is found, a search for the webpage on the Wayback Machine may yield a past version, which may be used to replace the dead link with an archived version.

When a broken link remains however, as is very common on the internet (especially between websites due to the difficulty of updating other websites linking to one's own), the visitor that clicks the dead link will get an HTTP 404 error, indicating the resource could not be found. The following tools try to rectify this error:

* The Linkgraph widget get the URL of the correct page based upon the old broken URL by using historical location information.
* The Google 404 Widget employs Google technology to 'guess' the correct URL, and also provides the user a Google search box to find the correct page.
* DeadURL.com gathers and ranks alternate urls for a broken link using Google Cache, the Internet Archive, and user submissions. Typing deadurl.com/ left of a broken link in the browser's address bar and pressing enter loads a ranked list of alternate urls, or (depending on user preference) immediately forwards to the best one.