The proposed format
The file lives at /llms.txt, or in a subfolder such as /docs/llms.txt to cover only part of a site. It is written in Markdown. The only required element is a top-level heading with the site or project name. Optional elements follow: a short summary in a blockquote, context paragraphs, then second-level sections containing lists of links, each with an optional note. A section titled Optional groups secondary links an agent can skip when it needs less context.
The proposal also suggests publishing a Markdown version of each page at the same URL with .md appended.
What llms.txt is not
It is not a counterpart to robots.txt: it neither allows nor blocks any crawler. Nor is it a standard adopted by search engines. Google states plainly that no new machine-readable files or AI text files are needed to appear in AI Overviews or AI Mode. Its real-world use is mostly by coding assistants and agents reading technical documentation.
Should you create one?
For a software company, an API or technical documentation, it is a small, useful investment: coding assistants and agents get a reliable table of contents. For a local small business site, other priorities come first, though the file costs almost nothing. If you publish one, list only canonical URLs, keep it in sync with the site and describe each page honestly, with no keyword stuffing. Treat it as documentation for machines, reviewed whenever you add or retire an important page.
Limits to keep in mind
No major AI company has publicly committed to reading the file when building answers, and its content is not verified: a forgotten llms.txt can describe services or prices that no longer exist. Before investing time, check your server logs to see whether any bots actually request /llms.txt, and which ones.