describedby

Describedby is a link relation type used in web documents to indicate that the linked resource provides a description of the resource that contains the link. It is registered in the IANA Link Relation Types registry and is recognized in standards governing HTML link elements and HTTP link headers.

Semantics: When a document includes a link with rel="describedby", the target describes the subject resource. The description may be in a machine-readable format such as JSON-LD, RDF, RDFa, or in a human-readable form such as HTML. The intended use is to separate descriptive metadata from the primary resource, allowing tools and clients to discover metadata without altering the resource itself.

Examples: In an HTML document, a head element might include: <link rel="describedby" href="https://example.org/resource-description.jsonld" />. In an HTTP response, a server could advertise a description with a header: Link: <https://example.org/resource-description.jsonld>; rel="describedby".

Rationale and interoperability: The describedby relation supports metadata extraction, accessibility enhancements, and data interlinking by providing a stable, discoverable location for descriptions. It is typically used alongside other link relations such as canonical, alternate, or describes. While not all user agents act on describedby links, they offer a standard mechanism for linking to descriptive metadata or documentation about a resource.

Notes: The usefulness of describedby depends on the availability and quality of the linked description document and the consumer’s ability to process its format.