llms.txt is a proposed convention: a Markdown file at the root of your site (yourdomain.com/llms.txt) that hands AI systems a short, curated map of what matters. Your key pages, products, and a one-line description of each. In a format that's trivial for a model to parse.
Think of it as a counterpart to robots.txt, but inverted: robots.txt says what crawlers may access; llms.txt says what they should pay attention to. Instead of making an engine infer your site's structure from messy HTML, you tell it plainly.
It's still an emerging standard. Adoption is growing but not universally honoured yet, so treat it as a low-cost, high-signal addition rather than a guarantee. For brands it's a cheap way to point AI at your best, most accurate content. (There's also llms-full.txt, a fuller single-file dump of site content for the same purpose.)