llms.txt is a proposed convention: a markdown file at a site's root that gives AI systems a concise, curated map of the site's most important content — robots.txt tells crawlers where they may go; llms.txt tells models what matters.
The file is plain markdown: a title, a one-paragraph summary, and sections of annotated links. Because LLM context windows are finite, the format's premise is curation — hand the model the twenty pages that represent the site, not the full sitemap.
Adoption is still emerging, but the cost is one static file, and sites that publish it make their structure legible to any agent that looks. This site's own copy lives at /llms.txt.