|This page in a nutshell: Link rot can kill poorly sourced citations, but steps may be taken to reduce or repair its effect. Do not merely delete cited information solely because the URL to the source does not work any longer.|
Like most large websites, Wikipedia suffers from the phenomenon known as link rot, where external links, often used as references and citations, gradually become irrelevant or broken (also called a dead link), as the linked websites disappear, change their content, or move. This presents a significant threat to Wikipedia's reliability policy and its source citation guideline.
The effort required to prevent link rot is significantly less than the effort required to repair or mitigate a rotten link. Therefore, prevention of link rot strengthens the encyclopedia. This guide provides strategies for preventing link rot before it happens. These include the use of web archiving services and the judicious use of citation templates.
Editors are encouraged to add an archive link as a part of each citation, or at least submit the referenced URL for archiving,[note 1] at the same time that a citation is created or updated.
However, link rot cannot always be prevented, so this guide also explains how to mitigate link rot by finding previously archived links and other sources. These strategies should be implemented in accordance with Wikipedia:Citing sources#Preventing and repairing dead links, which describes the steps to take when a link cannot be repaired.
Except for URLs in the External links section that have not been used to support any article content, do not delete cited information solely because the URL to the source does not work any longer. Recovery and repair options and tools are available. Verifiability does not require that all information be supported by a working link, nor does it require the source to be published online.