CorporisPublica:Link rot

Like most large websites, suffers from the phenomenon known as link rot, where external links, often used as references and citations, gradually become irrelevant or broken, as the linked websites disappear, change their content, or move. This presents a significant threat to '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.

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 CorporisPublica:Citing sources, which describes the steps to take when a link cannot be repaired.

Do not delete cited information solely because the URL to the source does not work any longer. CP:Verifiability does not require that all information be supported by a working link, nor does it require the source to be published online.

Except for URLs in the External links section that have not been used to support any article content, do not delete a URL solely because the URL does not work any longer. Recovery and repair options and tools are available.

Preventing link rot
As you write articles, you can help prevent link rot in several ways. The first way to prevent link rot is to avoid bare URLs by recording as much of the exact title, author, publisher, and date of the source as possible. If the link goes bad, this added information can help a future Wikipedian, either editor or reader, locate a new source for the original text, either online or a print copy. This likely wouldn't be possible with only an isolated, bare URL that no longer worked. Local and school libraries are a good resource for locating such offline sources. Many local libraries have in-house subscriptions to digital databases or inter-library loan agreements, making it easier to retrieve hard-to-find sources.

As you edit, if an article has bare URLs in its citations, fix them or at least tag the References section with linkrot as a reminder to complete citation details as above, and to categorize the article as needing cleanup.

Web archive services
A second way to prevent link-rot is to use a web archiving service. The two most popular services are the Wayback Machine, which passively archives many web pages, and WebCite, which provides on-demand web archiving. These services collect and preserve web pages for future use even if the original web page is moved, changed, deleted, or placed behind a pay wall. Web archiving is especially important when citing web pages that are unstable or prone to changes, like time sensitive news articles or pages hosted by financially distressed organizations. Once you have the URL for the archived version of the web page, use the  and   parameters in the citation template that you are using. The template will automatically incorporate the archived link into reference. However, not every web page can be archived. Webmasters and publishers may use a Robots exclusion standard in their domain to disallow archiving, or rely on complicated javascript, flash, or other code that can't easily be copied. In these cases, alternate methods of preserving the data may be available.

Alternate methods
Most citation templates have a  parameter that can be used to store text quotes of the source material. This can be used to store a limited amount of text from the source within the citation template. This is especially useful for sources that cannot be archived with web archiving services. It can also provide insurance against failure of the chosen web archiving service.



When using the quote parameter, choose the most succinct and relevant material possible that preserves the context of the reference. Storing the entire text of the source is not appropriate under fair use policies, so choose only the most important portions of the text that most support the assertions in the article.

A quote also helps searching for other on-line versions of the source in the event that the original is discontinued.

Where applicable, public domain materials can be copied to Wikisource.

Repairing a dead link
There are several ways to repair a dead link. Often web pages have simply moved, either in connection with a migration to a new server, or through general site maintenance. A site index is a useful place to locate the moved page. A search engine query using the title of the page, possibly with a search restriction to the same site, might also find the page. Using the examples from above, a Google search might look like: site:http://freakonomics.blogs.nytimes.com/ "Wall Street Journal Paywall Sturdier Than Suspected" Also, a Google search for some components of the dead link with punctuation removed is often fruitful, e.g. for groups.csail.mit.edu sFFT paper pdf lead to a page enabling this fix. A search for an unusual or unique-looking substring of the URL, such as just the filename at the end is often fruitful.

Failing that, check for archived versions of the page in the archiving services. Consult the Wayback Machine and the query page of WebCite and if applicable, the UK Government Web Archive. If you find an archived version, double-check to make sure that the material still supports the citation. It is also a good idea to consult the access date of the citation (if it was specified) to see how contemporaneous this archived version is to the link when it was cited.

Service under evaluation: http://archive.is. This is a new (2012) on-demand+crawling archiving service with a very short track record.
 * -Checking if a dead URL has been archived: prepend "archive.is/" to the URL. Example: http://archive.is/http://en.wikipedia.org/wiki/Wikipedia:Link_rot to check this page.
 * -On-demand: similar to WebCite. Saves full HTML+CSS, but strips Javascript. Saves full image of page as well.
 * -Crawler: This service crawls and archives offsite URLs. In many cases a now-deadlinked page may found at http://archive.is/
 * Note: This service should not be used alone, as its track record is too short. Use it along with another archive service until community consensus agrees it is persistent, well-funded, and reliable.

Mitigating a dead link
At times, all attempts to repair the link will be unsuccessful. In that event, consider finding an alternate source so that the loss of the original does not harm the verifiability of the article. Alternate sources about broad topics are usually easily located. A simple search engine query might locate an appropriate alternative, but be extremely careful to avoid citing mirrors and forks of itself, which would violate CorporisPublica:Verifiability.

Sometimes, finding an appropriate source is not possible, or would require more extensive research techniques, such as a visit to a library or the use of a subscription-based database. If that is the case, consider consulting with editors at CorporisPublica:WikiProject Resource Exchange, the CorporisPublica:Village pump, or CorporisPublica:Help desk. Also, consider contacting experts or other interested editors at a relevant WikiProject.

Keeping dead links
A dead, unarchived source URL may still be useful. Such a link indicates that information was (probably) verifiable in the past, and the link might provide another user with greater resources or expertise with enough information to find the reference. It could also return from the dead. With a dead link, it is possible to determine if it has been cited elsewhere, or to contact the person originally responsible for the source. For example, one could contact the Yale Computer Science department if http://www.cs.yale.edu/~EliYale/Defense-in-Depth-PhD-thesis.pdf were dead. Place dead link after the dead URL and just before the  tag if applicable, leaving the original link intact. Placing dead link auto-categorizes the article into Articles with dead external links project category, and into specific monthly date range category based on date parameter. Do not delete a URL because it has been tagged with dead link for a long time.

Bots

 * CP:STiki/Dead_links—Page reporting NEWLY added dead links, a component of the STiki project.
 * User:MerlLinkBot—purpose is to change links in articles which are outdated and can be successfully replaced by a new one. Submit requests for link updates to the bot's talk page.


 * User:Legobot—can mass tag links with . Requests can be made at User talk:Legoktm