llms.txt
An llms.txt file is a plain text index published at the root of a site that tells an AI client what the site is and which pages carry the answers, in the way robots.txt tells a crawler where it may go.
It is a proposed convention rather than a ratified standard, and support for it is uneven. That is the honest framing: nobody should rebuild anything around it, and nobody should expect a store to be found because of it.
What it does cheaply is remove ambiguity. A file that names your catalogue, your shipping policy and your returns policy, with a one line description of each, saves a client from inferring the shape of your site from its navigation.
Why it matters to a store
Low value and low cost, which is why it sits at the bottom of any fix list rather than off it. Fix the feed, the markup and the checkout first.