---
term: "Content negotiation"
canonical: https://citable.wiki/glossary/content-negotiation
also_known_as: "Proactive negotiation, server-driven negotiation"
license: CC BY 4.0
---

# Content negotiation

**Definition:** Content negotiation is the HTTP mechanism by which a client states which representations it prefers — using headers such as Accept, Accept-Language and Accept-Encoding — and the server picks the best available one for the same URL. For answer engines it lets one canonical URL return HTML to browsers and Markdown to a crawler that sends Accept: text/markdown.

HTTP defines content negotiation in [RFC 9110, section 12](https://www.rfc-editor.org/rfc/rfc9110#section-12). The common form is **proactive** (server-driven): the client sends `Accept` headers, optionally weighted with `q=` values; the server chooses a representation and names the headers it considered in `Vary`. If nothing acceptable exists it may answer `406 Not Acceptable` or fall back to a default. Compression (`Accept-Encoding`) and language (`Accept-Language`) have been negotiated this way for decades, so every cache and proxy already understands the mechanism.

The `text/markdown` media type has been registered since 2016 ([RFC 7763](https://www.rfc-editor.org/rfc/rfc7763)), which makes Markdown a legitimate representation to ask for.

An answer engine wants the text, not the chrome. Serving Markdown for `Accept: text/markdown` gives a crawler a compact representation of the same canonical URL with no navigation, scripts or consent banners to strip. This site does exactly that for every guide and glossary page, and also exposes the same Markdown at a `.md` suffix:

```bash
curl -H "Accept: text/markdown" https://your-site.example/glossary/content-negotiation
```

The one operational hazard is caching. Set `Vary: Accept` on both the HTML and the Markdown response, or a shared cache may hand Markdown to a browser. [Serving Markdown to LLMs](/guides/serving-markdown-to-llms) covers the implementation details.

## Frequently asked questions

### Should I use content negotiation or a .md URL to serve Markdown?

Both, if you can. A .md suffix is visible, linkable and easy to test in a browser; content negotiation keeps a single canonical URL. Whichever route serves Markdown, send Vary: Accept so caches keep the two representations apart, and point back to the HTML page with a canonical link header.

## Related guides

- [Serving Markdown to LLMs: content negotiation and .md endpoints](https://citable.wiki/guides/serving-markdown-to-llms)
- [llms.txt: what it is, how to write one, and whether it helps](https://citable.wiki/guides/llms-txt-what-it-is-and-how-to-write-one)

---

Source: https://citable.wiki/glossary/content-negotiation