llms.txt Validator
llms.txt Checker
Check your /llms.txt against the llmstxt.org format, test the links inside it, and confirm AI crawlers are allowed to read it. Free, no signup.
technical guide & best practices
What a Good llms.txt Looks Like
llms.txt is a Markdown file at the root of a site that gives language models a short, curated map of the pages worth reading, without the navigation, scripts and markup of the HTML. The format is a proposal from llmstxt.org, not a standard every AI system reads, so treat it as cheap insurance rather than a ranking factor. If you publish one, it should be correct: a file served as an HTML error page, or full of broken links, tells a model nothing useful.
Key Optimization Standards
frequently asked questions
Frequently Asked Questions
Do ChatGPT, Claude or Google actually read llms.txt?
Not reliably. None of the major AI search products has committed to reading it, and Google has said it does not use it for Search. Some AI coding tools and agents do fetch it when pointed at a site. It costs little to publish, but it will not replace crawlable pages, clear content or structured data.
What is the difference between llms.txt and llms-full.txt?
llms.txt is the short index: a title, a summary and links. llms-full.txt is an optional companion that contains the full text of those pages in one file, for tools that want everything at once. This checker reports whether llms-full.txt exists but validates only llms.txt.
Why does the checker say my llms.txt is an HTML page?
Your server answered /llms.txt with HTTP 200 but sent an HTML document, usually because a catch-all route serves the homepage or a styled 404 page for unknown paths. To a model that is not an llms.txt at all. Publish a real text file at that path.
Why are some links marked "not measured"?
The checker requests up to 25 links with a time limit. A link that did not answer in time is reported as not measured rather than broken, because a slow server is not proof of a dead page. Run the check again, or open the link yourself.