Wikipedia:Link rot
Like most large websites, Wikipedia suffers from the phenomenon known as link rot, where external links become dead, as the linked web pages or complete websites disappear, change their content, or move without HTTP redirection. This presents a significant threat to Wikipedia's reliability policy and its source citation guideline.
 | This help page is a how-to guide. It details processes or procedures of some aspect(s) of Wikipedia's norms and practices. It is not one of Wikipedia's policies or guidelines, and may reflect varying levels of consensus and vetting. |
 | This page in a nutshell: Steps may be taken to reduce or repair dead external links. |
In general, do not delete cited information solely because the URL to the source does not work any longer. Tools, procedures, and processes are available as outlined in this document.