Does llms.txt do anything?
Short answer: nobody has shown that it does. It costs almost nothing to publish and there is no evidence it moves anything, and those two facts are both true at once.
No confirmed mechanism · no engine has stated it reads this file
What it is
A proposed convention: a plain text file at the root of your site summarising what the site contains, intended to help language models find their way around. It was suggested by a developer in 2024 and picked up quickly because it is easy to understand and easy to sell.
What is actually known
No answer engine has published documentation saying it reads llms.txt, and no published study has shown a visibility change attributable to adding one. That is not proof it does nothing. It is an absence of evidence either way, and an absence of evidence is a poor foundation for a line item.
Compare it with robots.txt, which has a documented specification, published crawler names, and observable behaviour in your own server logs. You can prove robots.txt works by reading your logs. There is no equivalent observation available for llms.txt.
What several agencies say about it
Of the companies scored on this site, one describes llms.txt as the file AI reads to recommend you, presented on the page as settled fact. Another lists it among its technical deliverables. Neither cites a source, because there is not one to cite.
That is the useful part for a buyer. A page stating a mechanism nobody has demonstrated tells you how that company handles uncertainty generally, which is more informative than the claim itself. It is why falsifiability is one of the five things this site scores.
So should you publish one?
If it takes twenty minutes, publish it and forget it. The cost is trivial and the downside is nil. What you should not do is pay a monthly fee for it, accept it as evidence that work is happening, or let it sit in a proposal next to items that do have mechanisms, where it borrows their credibility.
Spend the attention on your robots.txt instead. That one is checkable, its effects are observable in your logs, and getting it wrong silently undoes everything else.