Some causes will result in the link failing to find any target at 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:  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 pertaining to the authorship of links include: Strategies pertaining to the protection of existing links include:  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 like Xenu's Link Sleuth. Automatic checking may not detect links that return a soft 404 or links that return an 200 OK response but point to content that has changed.