Definition
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.
In the report
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.
Worked example
One site of eight in the September 2026 runs had no llms.txt, and its readiness score was the lowest of the eight, 65, with three other checks missing beside it. The file is forty lines: the services page, the pricing page, the location page and the team page, each with one line saying what the page answers. The checker on this site reports whether the file exists, whether its links resolve and whether the AI crawlers can reach it; the generator writes a first draft from the site's own pages.
How to move it
Write it as an index, not a brochure: the pricing, the product and the comparison pages, one line each. Add llms-full.txt when the site's text is worth handing over whole.
Where it shows up
What is AI visibility? How often AI answer engines name a company when a buyer asks who to consider in its category, and whether they cite its own pages when they do. It is measured as a share of recorded answers, weighted by position in the list and by citation, across ChatGPT, Perplexity, Gemini and Google AI Overviews.
What is llms.txt and do I need one? 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.
See llms.txt measured on your site
Your website, region and work email. The score appears in about three minutes, and the report is a link you keep.