What llms.txt is
A plain-text file at the root of your site. It lists your pages with a one-line description of each. The format was proposed so that language models could find the useful parts of a site without crawling all of it. It sits next to robots.txt and sitemap.xml and replaces neither.
This site has one at /llms.txt. Bet Better, my sports analytics product, carries one that runs to 23,540 bytes. I ship the file. I do not charge for it. Neither should anyone else.
Who reads it
Google's John Mueller has said that no Google Search system reads or acts on llms.txt. No major AI provider has committed to reading it in production. Some crawlers fetch it. You can see which ones in your server logs. Fetching a file and using it are different things. Nobody with a large search or answer product has said they use it.
So the answer to the question in the title is: today, not much that you can measure.
Why I still put one up
- It takes about ten minutes.
- Writing it forces a one-line description of every page. That is a useful exercise on its own. It usually finds pages that can be merged.
- It costs nothing to serve and cannot hurt.
- If a provider does start reading it, yours is already there.
That is the whole case. A ten-minute task with no downside is worth doing. It is not worth a line item.
What gets you cited
The things that decide whether an answer engine names you are simpler than a new file format.
- Crawlers can reach you. Check robots.txt for the AI crawlers you are blocking by accident. Bet Better names ten AI crawlers in writing and sends a Content-Signal header alongside.
- Your answers are extractable. Retrieval is done on paragraphs. A page that buries its answer in paragraph nine gets skipped.
- Your details match everywhere they appear. Name, address, locations, services, on every page and in every listing.
- Schema is not the lever either. Google's own AI features documentation says there is no special schema.org structured data you need to add for AI Overviews or AI Mode. Ahrefs compared 1,885 pages that added JSON-LD against about 4,000 matched controls and found AI Overview citations down 4.6%.
Never pay for it
If a proposal includes llms.txt as a deliverable with a price next to it, ask what else in the proposal is priced the same way. Write yours this afternoon. Then spend the money on the paragraphs the engines lift.
If you want to know whether any of this is moving, AI search tracking is A$249 a month + GST. It tells you the number. It does not move it.