llms.txt is a plain-text file at your domain root that gives AI systems a clean, curated summary of your site: who you are, what you offer, and where the authoritative pages live. Adoption grew through 2025 and 2026, and since it costs an hour and cannot hurt, most businesses should publish one.
Robots.txt tells crawlers where they may go. llms.txt tells language models what your site actually is. It is a markdown file listing your identity, services, key facts and canonical pages, written to be ingested rather than rendered.
The standard is still informal and support varies by AI vendor, which is the honest caveat. But the asymmetry decides it: publishing one costs almost nothing, and when an assistant does read it, you have replaced guesswork with your own words.
What a good one contains
Your legal and trading name, one clear description, contact facts that exactly match your site and listings, a section per service with its canonical URL, and answers to the questions customers actually ask.
Keep it synchronised with your structured data. Contradictions between your llms.txt, your schema and your directory listings are precisely the signal that makes machines trust you less.