llms.txt is a Markdown file at the root of a site that tells AI tools what the site is and which pages matter most. Enter a domain to check the file against the llmstxt.org format, test a sample of its links and see whether an llms-full.txt version exists.
Table of Contents
The llms.txt format
The file starts with a level-1 heading with the site name, followed by a one-line summary in a blockquote. Sections use level-2 headings, and each section is a list of links in the form – [Page title](URL): short description.
A section named Optional holds links that tools may skip when they are short of space, such as archives or secondary pages.
What the validator checks
It confirms the file is served as text rather than an HTML error page, finds the heading, summary and sections, counts the link entries and how many have descriptions, and fetches up to eight linked pages to make sure they load. llms-full.txt, a single file with the full text of the key pages, is noted as optional.
Should you publish one?
llms.txt is a proposal, not a standard that every AI tool reads, but it costs little: a short, curated list of your most useful pages. Keep it in sync with the site, list canonical https:// URLs and keep descriptions factual.
llms.txt Validator at a glance
Official documentation: llmstxt.org specification.
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Frequently asked questions
Is llms.txt the same as robots.txt?
No. robots.txt says what crawlers may fetch; llms.txt is a guide to your content for AI tools. Allowing or blocking AI crawlers is still done in robots.txt.
Do search engines use llms.txt?
Google has said its Search systems do not use it. Some AI assistants and developer tools read it when they look at a site, which is where it helps.
What is the Optional section for?
Links under a level-2 heading named Optional are marked as secondary, so a tool with limited context can leave them out and still get the important pages.