A PLAIN ANSWER
What is llms.txt?
llms.txt is a short, plain-text file published at yoursite.com/llms.txt that summarizes what a website is and links to its most important pages, written specifically for AI systems to read instead of a human browsing the site. The specification lives at llmstxt.org, and this site publishes its own llms.txt as a working example.
WHY IT EXISTS
The problem it is trying to solve
AI systems can only read a limited amount of text at once, and a full website, with its navigation, footer, cookie banner and marketing copy, wastes most of that budget on things that are not the point. llms.txt is meant to hand over the short version directly: what the business is, what it offers, and where to find the pages that actually matter, without the AI system having to guess by scraping the whole site.
WHAT BELONGS IN ONE
The basic structure
- An H1 with the business or project name
The very first line, as plain markdown, naming what this is.
- A one-line summary in a blockquote
A single sentence describing what the business does and who it is for, the kind of thing you would say if someone asked “what is this, exactly” in one breath.
- Short sections linking to the pages that matter
Pricing, key services, contact information, and anything else an AI system would need to answer a question about the business accurately, each as a plain link with a short description.
- Facts worth quoting directly
Verified numbers, named credentials, or anything you would rather an AI system state correctly than infer from marketing language, written plainly so there is nothing to misread.
Honestly, nobody knows how much it helps yet
I will not oversell this one. As of now, there is no confirmed, public evidence that any major AI system actually reads or prioritizes llms.txt files when answering questions. The free health check treats it as a nice-to-have, not a make-or-break item, and that is the right way to think about it: cheap to publish, worth having, but not a substitute for a site that is fast, crawlable and has real structured data. Treat it as a small bet on where things might be heading, not a fix for anything more important.
Bill
Next step: for the bigger picture this fits into, see what AI visibility actually means. To understand which AI systems might read it in the first place, see AI crawlers, explained. Or run the free check to see whether your own site publishes one.