Wikipedia:Link rot

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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, 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.

Do not delete cited information solely because the URL to the source does not work any longer. WP: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[edit]

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. Optionally, also add the accessdate. 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[edit]

A second way to prevent link-rot is to use a web archiving service. The two most popular services are the Wayback Machine, which crawls and archives many web pages as well as having a form to suggest a URL to be archived,[note 1] 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 archiveurl= and archivedate= 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.

Robots.txt[edit]

A quirk in the way the Wayback Machine operates means archived copies of sites sometimes become unavailable, for example, the Freakonomics blog previously hosted at freakonomics.blogs.nytimes.com. Those URLs were then excluded from archiving by the New York Times' robots.txt file. This had the unfortunate effect of also rendering the previously archived content unavailable. But robots.txt changes can unhide that which previous changes have hidden, so do not delete an archiveURL solely because the archived content is currently unavailable. Luckily, in this case, not only can the content be found on a new site that is still open to archiving, but the site's robots.txt later changed to allow archiving again, and so the old archives are now unhidden (example).

Alternative methods[edit]

Most citation templates have a quote= 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 Wikipedia 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[edit]

There are several ways to try to repair a dead link, detailed below:

Site search[edit]

Often web pages have simply moved, either in connection with a migration to a new server, or through general site maintenance. A site index or site-specific search feature is a useful place to locate the moved page.

Search engine[edit]

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 web search (such as Google, Yahoo, etc.) might look like one of these:

site:freakonomics.blogs.nytimes.com/ "Wall Street Journal Paywall Sturdier Than Suspected"
site:nytimes.com/ "Wall Street Journal Paywall Sturdier Than Suspected"
"Wall Street Journal Paywall Sturdier Than Suspected"

Also, a search for some components of the dead link with punctuation removed is often fruitful; e.g. a search through Google for

groups.csail.mit.edu sFFT paper pdf

leads 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.

Internet archives[edit]

Check for archived versions of the page in the archiving services. If you find an archived version of the dead link, double-check to make sure that citation still supports the article text. It is also a good idea to consult the access date of the citation (if it was specified, or a history search for when it was added) to see how contemporaneous this archived version is to the link when it was cited.

The following archiving services are considered to be reliable:

The Mementos interface allows you to search multiple archiving services for archived versions of some pages with a single request using the Memento protocol. Unfortunately, the Mementos webpage interface removes any parameters which are included with the URL. If the URL contains a "?" it is unlikely to work properly when entered manually without changes. When entering the URL into the Menentos interface manually, the most common change needed is to change "?" to "%3F". While making only this change will not be sufficient in all cases, it will work most of the time. The bookmarklet in the table below will properly encode URLs such that searches will work. Mementos looks like it is, or at least will be, very convenient. However, if archives are not found at Mementos, it should not be the only site checked. Mementos can sometimes return no results when archives exist at sites which it normally includes. An example of this is trying to find archives of Battle of the Atlantic. As of April 2014, Archive.org reports it has 63 or 64 archives (https, http). Mementos reports 0 archives (https, http). Mementos usually finds archives at Archive.org, but sometimes Mementos does not even when archives exist. If you try Mementos first, don't assume that there really are no archives if Mementos reports that there are none.

There are many Internet archive projects in existence.

When multiple archive dates are available, try to use the one that is most likely to be the contents of the page seen by the editor who entered the reference on the |accessdate=. If that parameter is not specified, a search of the article's revision history can be performed to determine when the link was added to the article.

View the archive to verify that it contains valid page information. Sometimes archives are actually archives of the fact that the link is dead, or that the archiving failed. If this is the case, try using an archive from a different date. Usually dates closer to the time the link was placed in the Wikipedia page, or earlier, are more likely to show valid information. Different archiving sites should also be tried.

For most citation templates, archives are entered using the |archiveurl=, |archivedate= and |deadurl= parameters. The primary link is automatically switched to the archive when |deadurl=yes. This retains the original link location for reference.

Bookmarklets to check common archive sites for archives of the current page
(all open in a new tab or window)
Archive site Bookmarklet
Archive.org javascript:void(window.open('https://web.archive.org/web/*/'+location.href))
WebCite javascript:void(window.open('http://www.webcitation.org/query.php?url='+location.href))
Mementos interface javascript:void(window.open('http://www.webarchive.org.uk/mementos/search/'+encodeURIComponent(location.href)+'?referrer='+encodeURIComponent(document.referrer)))

The following archiving services are not permitted on the English Wikipedia:

Mitigating a dead link[edit]

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 Wikipedia itself, which would violate Wikipedia: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 Wikipedia editors at Wikipedia:WikiProject Resource Exchange, the Wikipedia:Village pump, or Wikipedia:Help desk. Also, consider contacting experts or other interested editors at a relevant WikiProject.

Keeping dead links[edit]

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[dead link] were dead. Place {{dead link}} after the dead URL and just before the </ref> 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 just because it has been tagged with {{dead link}} for a long time.

Automated tools[edit]

There have been bots that proactively automatically archived external URLs used in Wikipedia articles. None are currently working.

There have been bots (the semi-automated RjwilmsiBot (talk · contribs) ) that automatically identify and flag dead links with {{dead link}}. No bots currently attempt to repair dead links or add an archivedate= field to citations with just an archiveurl= field.

See also[edit]

Bots[edit]

External links[edit]

Notes[edit]

  1. ^ a b Using the web form at https://archive.org, enter a URL and click "browse history". This will either redirect to show the latest previously archived copy, present a box near the bottom of the page with a link inviting the user to "save this URL in the Wayback Machine", display a calendar showing the extent of previously archived content for that URL, or show an error message explaining why the URL cannot be archived. If archiving is attempted and ultimately successful, the archived copy usually becomes available within minutes.