Glossary
Link rot
Link rot is the loss of access to cited web content when a URL stops resolving or no longer serves the referenced material.
Provenance and citation
Link rot describes a citation failure in which a web address no longer reaches the referenced content. A related problem is content drift: the URL still works, but the page has changed. Both weaken an evidence trail if a claim depends only on a live link. A stable identifier can improve discovery, yet it does not guarantee that the cited version remains available.
In practice, evidence records include the URL, access date, page title and a lawful retained copy or archive reference where appropriate. A locator to the relevant passage helps future readers find the support in that version. Periodic link checks can reveal failures, but replacing a dead link with a current page does not prove that the old claim was supported.
For an organization defending an earlier decision, the relevant question is what the source said at the time, not just what its site says now. Retained source copies and content addresses help preserve that answer. Link rot is a preservation problem; source reliability and truth discovery address different questions about whether the original statement deserved belief.
Example
A Halden Therapeutics AG (fictional) notice URL returns 404 after a site redesign; the retained dated copy still permits review of the earlier citation.
How common it is
Link rot is measurable. A 2024 study by the Pew Research Center checked pages and links across several kinds of site and found that more than a third of the webpages that existed in 2013 were no longer accessible a decade later, and that a notable share of current news and government pages contained at least one broken link. The study also notes that the age of a page is a strong predictor of whether it is still reachable. Scholarly citations show similar decay, as the study by Klein and colleagues listed under the references documents for articles that cite web resources.
A broken link is the visible form of the problem. A subtler form is content drift: the address still works, but the page now says something different from what it said when it was cited. A reader following the link sees the new text and cannot tell that the citation no longer supports the claim. Both forms undermine a citation, and drift is harder to detect because nothing visibly fails.
Defences, in order of strength
The strongest defence is to hold a copy of the source at the time of use, as described under retained source copy, and to cite the copy by its digest, as in content addressing. A weaker defence is to cite a public archive snapshot, using the Internet Archive's Wayback Machine or a Memento-compliant archive: the Memento protocol, RFC 7089, lets a client ask for the version of a resource as of a date, across archives. A weaker defence still is monitoring: periodic checks that cited URLs return the same content, with an alert when they do not.
Monitoring has a cost, and a sensible policy sets its frequency by how much a claim matters. Check high-stakes citations often and the rest rarely. Record each check, with the response status and a digest of the content, so that drift is detected as a change of digest and not by someone noticing. The Wikipedia article on link rot gives a general overview of causes and mitigation.
A worked example
A knowledge base cites 4,000 web pages as support for its statements. A quarterly check requests each URL and compares the response with the stored digest. In one run, 120 pages return errors, 310 redirect to a generic home page, and 85 return a page whose digest has changed. The 120 are the easy cases: the stored copies serve as evidence and the citations are marked as dead links with copies. The 310 redirects are the dangerous ones, since a naive check treats a successful response as a pass; they are flagged because the digest changed and the new content does not contain the cited passage. The 85 changed pages are compared by text difference, and the claims for which the cited passage is gone go to review. The numbers are illustrative; the pattern of three failure modes is general.
Checks a reviewer can run
Ask what proportion of citations have a retained copy. Ask how a citation is tested for drift and not only for a response code. Ask what the system does when a cited page changes: whether the claim is flagged, re-reviewed or left alone. Ask whether the policy distinguishes high-stakes citations from others. Sample twenty citations, open the stored copies, and confirm that each contains the passage cited.
Related terms and boundaries
Link rot is the main reason for keeping a retained source copy and for citing by digest. It threatens every sentence-level citation, erodes the support for a claim, and must be accounted for in point-in-time reproducibility, since a result that cannot retrieve its sources cannot be reproduced.
Common misreadings
- Replacing an old citation with a changed current page.
- Assuming a working URL serves unchanged content.
- Recording no access date or source version.
Appears in
- Document citation vs sentence citation
A document citation identifies an artifact; a sentence citation locates the specific statement supporting a claim.
- Detecting source drift
Compare current source content with the retained cited version and reassess changed support.
- Retaining source copies
Preserve the material actually read, subject to rights, and bind its citation with a content digest.
- Data Catalog Vocabulary (DCAT)
An RDF vocabulary for describing datasets and catalog distributions.
- Digital Object Identifier (DOI)
A persistent identifier for a registered digital object or other referent.
References
- Klein et al. (2014), Scholarly Context Not Found: One in Five Articles Suffers from Reference Rot, PLOS ONE 9(12).
- Pew Research Center (2024), When Online Content Disappears.
- IETF (2013), RFC 7089: HTTP Framework for Time-Based Access to Resource States (Memento).
- Internet Archive, Using the Wayback Machine.
- Wikipedia, Link rot.
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Enquiry
Where does "Link rot" bear on a decision of yours?
This entry sits under provenance and citation. If a decision in your organization turns on it, send the entity concerned, the sources you fuse to describe it and who may read which of them. We reply with what a first record would cover.
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