llms.txt: the AI sitemap, explained

llms.txt is a proposed file format that gives AI assistants a structured summary of your website's content. Think robots.txt for crawl rules, sitemap.xml for URL discovery, llms.txt for AI summarization. It's not yet a hard standard, but it costs nothing to ship and several AI providers are starting to honor it.

The format

Markdown file served at /llms.txt. First line is an H1 with your site title. Then a blockquote with a one-paragraph description. Then sections with bulleted links to key URLs and one-line descriptions.

# Acme

> Acme builds [thing] for [audience]. Founded in [year], headquartered in [place].

## Product
- [Pricing](https://acme.com/pricing): three tiers, $39 / $99 / $299 per month
- [Docs](https://docs.acme.com): full API and integration documentation

## Resources
- [Blog](https://acme.com/blog): tactical guides on [category]

Who honors it

As of mid-2026: Anthropic's Claude and Perplexity have both publicly said they respect llms.txt for context discovery. OpenAI hasn't formally endorsed it but their crawler appears to fetch it. Independent indices and AI-focused search engines increasingly use it as a structured signal.

Should you ship one?

Yes. It costs 30 minutes to write and serves three purposes:

• Some AI crawlers actually use it.
• You're forced to articulate what your site actually offers in a few hundred words, which is a useful exercise.
• If the standard catches on, you're ahead.

The companion file

Many sites also publish /llms-full.txt — a longer markdown document with the full canonical content of the site, optimized for AI consumption. Useful for docs sites in particular: it gives the LLM one URL to fetch instead of dozens.

What it isn't

llms.txt is not a magic visibility booster. If your brand isn't in the citation sources LLMs trust, llms.txt won't fix that. It's a hygiene file, not a strategy.