What is “link rot”?
Link rot is real, it is common, and it is pervasive. Link rot is essentially the process by which hyperlinks cease to function, usually because the web page or server they point to has moved or has become permanently unavailable. It has existed since the internet began.
Web pages are ephemeral
Examples of link rot are far and wide. One study found that 70% of links in Harvard Law Review and 50% of links within the United States Supreme Court opinions are no longer viable.  If we are to take the internet as a primary resource seriously, then we seriously need to think about undertaking a better way of long-term preservation of link contents.
Link rot is pervasive
There seems to be no top-level domains (TLDs) that are free of link rot. In one study that looked at 720,000 pages on a daily basis, in only 11 weeks, 15% of .net domains had rotted links, 10% of .com, .org domains had rotted links, and 5% of .edu links had rotted. Another study found that within 24 months, 50% of .com domains and 20% of .gov domains were no longer viable. 
What is the half-life of a link?
There are a number of sources that have looked into the half-life of a website. Random web pages seem to have a half-life of about 2 years , legal citations 1.4 years , communication articles 3.2 years . Digital libraries have a much higher persistance, as their half-life is about 24.5 years .
How stop link rot
Link rot can be combated in several ways.
- Use a digital object identifier which provides persistent and actionable identification. The a website under a DOI changes, it can be changed in the DOI service so that the unique DOI identifier always links to the most up-to-date material.
- Use a permanent web framework. Our current web protocol has many nodes of failure, while newer hypermedia frameworks seek a more distributed protocol with builtin content identies that would allow data to permanently be available.
- Only link to archiving sites like the Internet Archive or perma.cc. My little program I’ve written helps to combat link rot by providing a simple and easy way to convert all your links to an archived link.
My attempt at stopping link rot.
In an effort to try to stop link rot, I’ve created a simple web app that convers all links to archivable links. The code is available at http://github.com/schollz/prevent-link-rot. Here is a snapshot:
Try the demo here.
- Zittrain, Jonathan, Kendra Albert, and Lawrence Lessig. “Perma: Scoping and addressing the problem of link and reference rot in legal citations.” Legal Information Management 14.02 (2014): 88-99.
- Markwell, John, and David W. Brooks. ““Link rot” limits the usefulness of web‐based educational materials in biochemistry and molecular biology*.” Biochemistry and Molecular Biology Education 31.1 (2003): 69-72.
- Koehler, Wallace. “Web page change and persistence—A four‐year longitudinal study.” Journal of the American Society for Information Science and Technology 53.2 (2002): 162-171.
- Rumsey, Mary. “Runaway Train: Problems of Permancence, Accessibility, and Stability in the Use of Web Sources in Law Review Citations.” Law Libr. J. 94 (2002): 27.
- Dimitrova, Daniela V., and Michael Bugeja. “The half-life of internet references cited in communication journals.” New Media & Society 9.5 (2007): 811-826.
- Nelson, Michael L., and B. Danette Allen. “Object persistence and availability in digital libraries.” D-Lib magazine 8.1 (2002): 1082-9873.
- Perkel, Jeffrey M. “The trouble with reference rot.” Nature 521.7550 (2015): 111-112.