Markdown mirror sends canonical Link header
When an agent fetches the markdown mirror, it needs a way to find its way back to the canonical HTML page (for example, to link a citation). The Link header with rel="canonical" is the HTTP equivalent of <link rel="canonical"> for non-HTML responses.
How the check decides
The check inspects the markdown mirror’s response Link header and asserts it contains a rel="canonical" (or rel=canonical) parameter. Fails if no Link header is present or it lacks rel=canonical. Returns N/A if no mirror exists.
How to implement it
Configure the response that serves your .md mirrors to emit a Link header pointing at the HTML page. On Vercel, Netlify, Cloudflare, etc. this is a one-line custom-headers rule.
Pass
HTTP/1.1 200 OK
Content-Type: text/markdown; charset=utf-8
Link: <https://example.com/docs/install>; rel="canonical"
# Install a14y
...
Fail
HTTP/1.1 200 OK
Content-Type: text/markdown; charset=utf-8
# Install a14y
...