Module 3: Checkpoint 4—Aliasing a resource

Conformance: Mandatory


When more than one URL exists for a resource, all alternate URLs must redirect to the primary URL using an appropriate HTTP status message.

Benefits of conformance

  • Short and memorable URLs can be created allowing easy promotion of important content.
  • Search engines will be able to consolidate page rankings accurately to the correct URL.
  • Consistent, quality experience for users of the site.

Risks of non-conformance

  • Search engines may split page rankings between two duplicate resource URLs.
  • Search engines may remove a site from their search results pages entirely if duplicate content is found on a site.
  • Potential user confusion when a duplicate resource is found to exist at multiple URLs, possibly from multiple search results.
  • If redundant duplicate resources are used maintenance overhead is incurred to keep all copies up to date.

Implementation advice


It can sometimes be useful to provide more than one URL that references the same resource; this is referred to as URL aliasing. It is important to remember that for every resource there should be only one canonical (primary) URL; any aliases for the same resource should redirect to the canonical URL.

For example: If a content page is exposed at and a preferred (canonical) domain should be chosen and all resources from the non-preferred domain should be redirected to the relevant resource under the preferred domain.

See the Aliasing a resource section from the HTTP status message guidelines for further information about how to meet this requirement.