# No markdown content negotiation in Next.js

> How to fix no markdown content negotiation in Next.js — with the exact fix and copy-paste code.

_Category: AI readiness · Detector `aeo` · Check `markdown-negotiation-missing` · Severity: info_

When an agent requests your page with `Accept: text/markdown` and gets HTML back, it has to parse the full DOM — navigation, scripts, styling — to recover the content. Offering a markdown representation of the same URL hands agents clean, structured text directly. It’s an advanced, optional signal, but a strong one for agent-first sites and docs.

## The fix for Next.js

Branch on the `Accept` header inside a Route Handler (or Middleware) and return the markdown source with the right content type and `Vary` header.

_app/blog/[slug]/route.ts (or middleware)_

```ts
export async function GET(req: Request, { params }) {
  const post = await getPost((await params).slug)
  if (req.headers.get('accept')?.includes('text/markdown')) {
    return new Response(post.markdown, {
      headers: { 'Content-Type': 'text/markdown; charset=utf-8', Vary: 'Accept' },
    })
  }
  return new Response(renderHtml(post), { headers: { 'Content-Type': 'text/html' } })
}
```

### Steps

1. Detect `Accept: text/markdown` on your content routes
2. Return the markdown representation with a `text/markdown` content type
3. Send `Vary: Accept` so caches don’t mix HTML and markdown responses

## How VibeCheck detects it

The `aeo` detector flags this live in the browser and reports it to the widget's Problems list — and to your coding agent over MCP.

- **Issue string:** `No markdown content negotiation`
- **Threshold:** A request with Accept: text/markdown still returns an HTML content type

## FAQ

### Is markdown negotiation required?

No — it’s an optional, advanced AEO signal, most valuable for docs and agent-facing sites. VibeCheck reports it as info, not an error. Skip it if your content isn’t markdown-backed.

### Why send `Vary: Accept`?

So shared caches and CDNs store the HTML and markdown responses separately per `Accept` header, instead of serving one to a client that asked for the other.

### How is this different from `llms.txt`?

`llms.txt` is one static index of your key content for LLMs; markdown negotiation serves a clean markdown version of any URL on request. They complement each other — `llms.txt` points agents at the content, negotiation delivers it without the DOM noise.

See the general, framework-agnostic fix: https://vibecheck.wcgw.fun/fix/missing-markdown-negotiation.md

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Fix guide from VibeCheck — https://vibecheck.wcgw.fun/fix/missing-markdown-negotiation. Full site index for LLMs: https://vibecheck.wcgw.fun/llms.txt