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CONCEPT Cited by 1 source

Link response header (RFC 8288)

Definition

Link: is an HTTP response header standardised as RFC 8288. Each value carries a URL plus a rel="..." relation type, expressing a typed link from the current resource to another resource.

HTTP/1.1 200 OK
Link: </.well-known/api-catalog>; rel="api-catalog"
Link: </sitemap.xml>; rel="sitemap"
Link: </feed.xml>; rel="alternate"; type="application/rss+xml"

Unlike links buried in HTML (which require a markup parser and are visible only to clients that render HTML), the Link: header is part of the HTTP response itself — discoverable by any client capable of reading HTTP headers.

Why it matters for agents

For an autonomous agent, protocol-level discovery is qualitatively better than markup-level discovery:

  • No HTML parsing required. A HEAD request with a parser for a few comma-separated values is sufficient.
  • Always available. Even non-HTML resources (JSON APIs, binary downloads, RSS feeds) can advertise related resources via Link:.
  • Lower cost at scale. A bot scanning millions of sites pays much less for headers-only discovery than for full-page fetch + parse.
  • Aligns with well-known URIs. Link: rel="api-catalog" paired with the target at /.well-known/api-catalog gives the agent a two-layer discovery: from any endpoint, find the directory; from the directory, find every API.

Cloudflare's 2026-04 framing

Cloudflare names the Link: header as the Agent-Discovery primitive that doesn't require parsing HTML:

"Unlike links buried inside HTML, the Link header is part of the HTTP response itself, which means an agent can find links to resources without having to parse any markup."

The example given — Link: </.well-known/api-catalog>; rel="api-catalog" — shows the header carrying the API Catalog URL, which is one of the more valuable discovery signals for an agent wanting to take actions against the site.

Agent Readiness Score scope

Graded under the Agent Discovery dimension of Agent Readiness Score, alongside robots.txt and sitemap presence. Named as one of three protocol-level resource-discovery mechanisms an agent can use to enumerate a site's content.

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