llms.txt
llms.txt is a proposed, publicly accessible text file in a website's root directory that summarises for AI systems, in a simple structured form, which content and subpages are particularly relevant for automated requests.
In practice
Unlike robots.txt, llms.txt does not control technical access; it offers curated orientation for language models – a young, voluntary standard without official support from every AI provider, but one that is becoming established as a practical AEO building block.