# HTTP Link header

Relations declared in headers, readable without parsing the body.

**[Discoverability](/docs/discoverability)** · checked on every URL · 5 checks that can fail it

A `Link` header is the cheapest thing an agent can read: it arrives with the response and needs no HTML parse. A malformed field is worse than none, because a conforming parser drops the whole header rather than the bad part.

## Adoption

**Web baseline** (L4)

Standard equipment on the web. Its absence is the exception rather than its presence. Direction of travel: ► flat, as of 2026-07-28.

RFC 8288 is standard HTTP machinery, used for canonical, preload and API pagination.

## What we check

Absence is never a finding: every check below runs only once `linkHeaderPresent` is true, so a site that has not
adopted this is not assessed on it and appears in no report.

| Check | Kind | Raises | On whose authority |
|---|---|---|---|
| `linkHeaderMalformedSyntax` | medium severity | conformance, usability | specification (RFC 8288) |
| `linkHeaderMissingRel` | medium severity | conformance, usability | specification (RFC 8288) |
| `linkHeaderInvalidUri` | medium severity | conformance, usability | specification (RFC 8288) |
| `linkHeaderDuplicateRel` | low severity | conformance, usability | specification (RFC 8288) |
| `linkHeaderInvalidRel` | low severity | conformance, usability | specification (RFC 8288) |

## Specifications

| Document | Revision | Kind |
|---|---|---|
| [RFC 8288 — Web Linking](https://www.rfc-editor.org/rfc/rfc8288) | RFC 8288 | specification |
| [RFC 9110 §5.6.2 / §5.6.4 — tokens and quoted strings](https://www.rfc-editor.org/rfc/rfc9110) | RFC 9110 | specification |
| [specification.website — agent-readiness link patterns](https://specification.website/spec/agent-readiness/) | living document | guidance |

Last re-read against the published documents: 2026-08-12.