A Markdown file at your site's root that tells language models what the site is and which pages are worth reading: a name, a one-line summary, and a short list of links. It is an index, not a brochure. It costs ten minutes, it is one of the thirteen checks in the report, and the checker on this site writes a starting one from your pages.
What goes in it
The pages a buyer would want an engine to read: pricing, the product or service pages, comparisons, the about page. One line each, with the link. Leave out the blog archive. llms-full.txt is the optional companion: the text of those pages in one file, for engines that want it whole.
What it does and does not do
It does not make an engine name you; the sources decide that. It makes the engine's read of your site accurate when it does fetch you, which is what the 'cited your own site' column in the report measures. Adoption by the engines is uneven and undocumented; the cost is small enough that the question is not worth the debate.
The term behind it: llms.txt
A Markdown file at a site's root that tells language models what the site is and which pages are worth reading. An index; llms-full.txt is the optional single file with the pages' text.
One of the thirteen checks: present at the root, in Markdown, with a name, a one-line summary and the pages worth reading. The checker on this site reads yours and, if there is none, writes a starting one. llms.txt, in full.
Read next
llms.txt checker · llms.txt · AI search starter kit: five files from your own pages
Ask it about your own company
Your website, region and work email. The score appears in about three minutes, and the report is a link you keep.