Markdown negotiation caching (Vary)
Without Vary: Accept, a cache may return the wrong response, sending browsers Markdown instead of HTML.
- Category
- Content accessibility
- Standard
- Recommended
What it checks
When the page serves Markdown through content negotiation, the same URL returns
two different bodies depending on the Accept header. The Vary response
header tells caches and CDNs to store them separately.
This check reuses the request made by
Markdown content negotiation.
If Markdown was negotiated, it looks for Accept in the response’s Vary
header. If Markdown was not negotiated, there is nothing to cache separately and
the check does not apply.
Results
| Status | When |
|---|---|
| Pass | Markdown is negotiated and the response includes Vary: Accept |
| Fail | Markdown is negotiated but Vary does not include Accept |
| N/A | The page does not negotiate Markdown |
How to fix
Add Accept to the Vary header on every response from a URL that
negotiates, both the HTML and the Markdown:
Vary: Accept, Accept-EncodingWithout it, a CDN can serve its cached HTML to an agent that asked for Markdown, or its cached Markdown to a browser.