What Is llms.txt? The AI-Agent Index File, Explained

Updated 2026-06-23

TL;DRllms.txt is a simple Markdown file you put at yoursite.com/llms.txt. It gives AI agents and AI search engines a clean, curated map of your site — a short description plus links to your most important pages. It's to AI agents what sitemap.xml is to search crawlers. It won't fix bad content, but it makes a good site far easier for AI to understand and cite.

What llms.txt is

llms.txt is a plain-text (Markdown) file served at the root of your domain — https://example.com/llms.txt — that tells large language models and AI agents what your site is about and where the important content lives. Think of it as a curated, human-written index for machines: a short description of your site, followed by a tidy list of your key pages with one-line explanations.

It is not the same as robots.txt (which controls crawling) or sitemap.xml (a raw list of every URL). llms.txt is a short, opinionated guide that points an AI to the few pages that actually matter.

Why it matters in 2026

AI search now answers a large and growing share of informational queries. When ChatGPT, Perplexity, or an autonomous agent lands on your site, it has a limited context window and limited patience. A clean llms.txt:

tells it, in one read, what your site is and who it's for;
points it straight to your best, most citable pages;
reduces the chance it misreads or ignores you.

Most sites still don't have one — which means publishing a good llms.txt is a cheap, early-mover advantage.

What a good llms.txt looks like

# Your Site Name

> One or two sentences: what this site is, who it's for, what makes it credible.

## Key pages
- Product: https://example.com/product
  What it is, in one line.
- Pricing: https://example.com/pricing
  Plans and what's included.
- Docs: https://example.com/docs
  Developer documentation and API reference.

## Optional
- Lower-priority sections an AI with limited context can skip.

How to write one (5 steps)

Start with a one-line summary of your site in a blockquote.
List only your most important pages — not every URL.
Add a one-line description under each link so the AI knows why it matters.
Group with ## Headings (e.g. Key pages, Docs, Optional).
Serve it at /llms.txt as text/plain or text/markdown and keep it updated.

Frequently asked questions

Does llms.txt replace my sitemap? No. Keep your sitemap.xml for search crawlers. llms.txt is a curated layer on top, written for AI comprehension.

Will it instantly boost my AI visibility? It's a helper, not magic. It makes a good site easier to understand and cite. It won't rescue thin content.

Is there an official standard? It's a community convention that gained real traction through 2025–2026. The format above is the widely-used shape.

Want to know if your whole site is agent-ready, not just your llms.txt? Run it through the free Agent Readiness Checker.