llms.txt is a proposed convention, not a standard: a markdown file at yoursite.com/llms.txt that lists your most important pages with a line of context each, so a model reading your site has a clean map instead of a navigation menu. No major assistant has publicly committed to reading it, and nobody has published evidence that having one changes whether you get cited.
Add it anyway, for a reason that has nothing to do with the crawlers. The rest of this is that reason, and what to put in the file.
What actually goes in it
A heading with the name of the site, one paragraph saying what the business is and who it is for, then grouped lists of links with a short description after each. The pages worth listing are the ones you would want quoted: what you sell, how you work, the evidence, and the writing that answers real questions. Not your privacy policy.
Ours is at roasdept.com/llms.txt, and it is deliberately short. A file that lists every URL on the site is a sitemap, and there is already a sitemap.
Why we add it even without evidence it is read
Because writing it forces the argument that most sites have never had. You cannot describe your business in one paragraph for a model without discovering whether you can describe it in one paragraph for a person. Half the time the file cannot be written until the homepage is fixed, and that is the finding.
The value is in being made to say, in one paragraph, what the business is. Most sites fail that test the first time.
What it does not do
It does not get you cited. It does not make a thin page quotable, it does not substitute for the crawlers being allowed in, and it will not move a ranking. If somebody has sold you an AI visibility package whose deliverable is an llms.txt file, you have bought a text file. The work that moves citations is the passage on the page and the third party mentions around it.
How to check yours in a minute
Open yoursite.com/llms.txt. If it 404s you do not have one. If it exists, read the first paragraph out loud and ask whether a stranger would know what you sell and who it is for. Then check every link in it resolves, because a file full of links to pages you have since renamed is worse than no file at all.
What we do with it
We write one for every site we run, after the pages themselves are right, and we treat it as the last ten minutes of the job rather than the deliverable. The channel it belongs to is on the SEO and GEO page.