The rate of Link Rot is a subject of study and research due to its significance to the internet's ability to preserve information. Estimates of that rate vary dramatically between studies. Information professionals have warned that link rot could make important archival data disappear, potentially impacting the legal system and scholarship.

Commonly, broken website links may immediately redirect the user to the home page of the website, confusing users even more and resulting in it being difficult to obtain the URL of the broken link.

Prevalence

Several studies have examined the prevalence of link rot within the World Wide Web, in academic literature that uses URLs to cite web content, and within digital libraries.

Causes

Link rot can result from several occurrences. A target web page may be removed. The server that hosts the target page could fail, be removed from service, or relocate to a new Domain name. As far back as 1999, it was noted that with the amount of material that can be stored on a hard drive, "a single disk failure could be like the burning of the library at Alexandria."

A domain name's registration may lapse or be transferred to another party. Some causes will result in the link failing to find any target and returning an error such as HTTP 404. Other causes will cause a link to target content other than what was intended by the link's author.

Other reasons for broken links include:

• the restructuring of websites that causes changes in URLs (e.g. domain.net/pine_tree might be moved to domain.net/tree/pine)
• relocation of formerly free content to behind a paywall
• a change in server architecture that results in code such as PHP functioning differently
• dynamic page content such as search results that change by design
• deletion of the target page and/or its content
• the presence of user-specific information (such as a login name) within the link
• deliberate blocking by content filters or firewalls
• the expiration of a domain name registration

Prevention of Link Rot

Strategies for preventing link rot can focus on placing content where its likelihood of persisting is higher, authoring links that are less likely to be broken, taking steps to preserve existing links, or repairing links whose targets have been relocated or removed.

The creation of URLs that will not change with time is the fundamental method of preventing link rot. Preventive planning has been championed by Tim Berners-Lee and other web pioneers.

Strategies for the authorship of links include:

• linking to primary rather than secondary sources and prioritizing stable sites
• avoiding links that point to resources on researchers' pages
• using clean URLs or otherwise employing URL normalization or URL canonicalization
• using permalinks and persistent identifiers such as ARKs, DOIs, Handle System references, PURLs, or content addressing
• avoiding linking to documents other than web pages
• avoiding deep linking
• linking to web archives such as the Internet Archive, WebCite, and Archive.today, Perma.cc, Amber, or Arweave

Strategies for the protection of existing links include:

• using redirection mechanisms such as HTTP 301 to automatically refer browsers and crawlers to relocated content.
• using content management systems that can automatically update links when content within the same site is relocated or automatically replace links with canonical URLs
• integrating search resources into HTTP 404 pages

The detection of broken links may be done manually or automatically. Automated methods include plug-ins for content management systems as well as standalone broken-link checkers such as Xenu's Link Sleuth. Automatic checking may not detect links that return a soft 404 or links that return a 200 OK response but point to content that has changed.