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Discovering llms.txt and Markdown versions

How an agent finds llms.txt and the Markdown version of a page under the second edition - rel=alternate and rel=describedby, the Link header, files in subpaths

added in the second edition, August 10, 2026

How it works

Section titled “How it works”
What an agent learns from a page
  1. A page/docs/install.htmlthe agent arrived here by a link
  2. rel=alternateMarkdown version/docs/install.html.mdthe same text without styling
  3. rel=describedbyThe covering file/docs/llms.txta map of the whole section

Two ways to declare the relations

Section titled “Two ways to declare the relations”
install.html
<head>
  <title>Installation</title>
  <link rel="alternate" type="text/markdown" href="/docs/install.html.md">
  <link rel="describedby" href="/docs/llms.txt">
</head>

The header has two advantages. It can be added in the web server or CDN configuration without touching any page. And it works for files that have no <head>, such as the Markdown files themselves.

Files in subpaths

Section titled “Files in subpaths”

llms.txt does not have to sit in the site root. A file covers the addresses under its path: /docs/llms.txt describes everything in /docs/.

When several files apply to a page, an agent takes the most specific one.

Page Files that apply The one used
/docs/api/auth.html /llms.txt, /docs/llms.txt, /docs/api/llms.txt /docs/api/llms.txt
/docs/guide.html /llms.txt, /docs/llms.txt /docs/llms.txt
/blog/post.html /llms.txt /llms.txt

The same rule lets those who control only a part of a site take part: a project on shared hosting with an address like example.github.io/project/, for instance.

The address of the Markdown version

Section titled “The address of the Markdown version”

The second edition allows two forms.

Page Appended form Replaced form
/docs/page.html /docs/page.html.md /docs/page.md
/docs/ /docs/index.html.md /docs/index.md

Whichever form a site picks, rel="alternate" saves the agent from guessing.

Why not /.well-known/

Section titled “Why not /.well-known/”

There is a standard place for metadata files: the /.well-known/ directory. The author of the proposal declined it for one reason: such addresses exist only at the site root. An llms.txt describes the path it sits in, and a single root location cannot express that.

In practice

Section titled “In practice”

What is known and what is not

Confirmed

  • The relations are described in the text of the second edition.
  • rel="alternate" pointing to a Markdown version is found on several documentation sites, Anthropic among them.
  • In our check of 46 sites on October 3, 2026, rel="describedby" was found on one: Cursor.

Not proven

  • That agents already read these relations at scale. The edition is recent.

What it does not mean

  • Some platforms send headers of their own: rel="llms-txt", rel="llms-full-txt", X-Llms-Txt. They are not part of the second edition.

Next

Section titled “Next”