---
title: "Markdown negotiation caching (Vary) · Sitebulb Labs"
description: "Without Vary: Accept, a cache may return the wrong response, sending browsers Markdown instead of HTML."
url: https://labs.sitebulb.com/docs/checks/content-accessibility/markdown-negotiation-vary/
---

# Markdown negotiation caching (Vary)

Without Vary: Accept, a cache may return the wrong response, sending browsers Markdown instead of HTML.

- Category

  [Content accessibility](https://labs.sitebulb.com/docs/checks/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](https://labs.sitebulb.com/docs/checks/content-accessibility/markdown-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:

```txt
Vary: Accept, Accept-Encoding
```

Without it, a CDN can serve its cached HTML to an agent that asked for Markdown, or its cached Markdown to a browser.