The idea borrows from robots.txt and sitemap.xml. Where robots.txt controls crawler access, llms.txt is meant to help language models find and prioritize your key pages by listing them in clean Markdown, sometimes with short descriptions and links to plain-text versions.
Adoption is early and support varies by engine, so treat llms.txt as a low-cost, forward-looking signal rather than a guaranteed ranking factor. Publishing one is cheap and aligns with the broader goal: make your most important content trivial for a model to locate and read.