Link rot

Link rot (or linkrot) is the process by which hyperlinks on individual websites or the Internet in general point to web pages, servers or other resources that have become permanently unavailable. The phrase also describes the effects of failing to update out-of-date web pages that clutter search engine results.

Link rot is also called "link death", "link breaking" or "reference rot". A link that does not work any more is called a "broken link", "dead link", or "dangling link". Formally, this is a form of dangling reference: The target of the reference no longer exists.

One of the most common reasons for a broken link is that the web page to which it points no longer exists. This frequently results in a 404 error, which indicates that the web server responded but the specific page could not be found. Another type of dead link occurs when the server that hosts the target page stops working or relocates to a new domain name. The browser may return a DNS error or display a site unrelated to the content originally sought. The latter can occur when a domain name lapses and is reregistered by another party. Other reasons for broken links include:

The 404 "Not Found" response is familiar to even the occasional web user. A number of studies have examined the prevalence of link rot on the web, in academic literature, and in digital libraries. In a 2003 experiment, Fetterly et al. discovered that about one link out of every 200 disappeared each week from the Internet. McCown et al. (2005) discovered that half of the URLs cited in D-Lib Magazine articles were no longer accessible 10 years after publication, and other studies have shown link rot in academic literature to be even worse (Spinellis, 2003, Lawrence et al., 2001). Nelson and Allen (2002) examined link rot in digital libraries and found that about 3% of the objects were no longer accessible after one year. In 2014, bookmarking site Pinboard's owner Maciej Cegłowski reported a “pretty steady rate” of 5% link rot per year.

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