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Free llms.txt Validator
Check a live llms.txt by domain, or paste a draft. The validator tests it against the llmstxt.org format — title, summary, sections, link syntax, URLs — and tells you exactly what to change.
What the validator checks
- H1 title — the first line must be
# Name. It's the only element the format requires, so a missing or misplaced H1 is a failure. - Summary blockquote — a
>line right after the title. Optional in the proposal, but it's the most useful sentence in the file. - H2 sections and heading levels — content is grouped under H2s; the format doesn't define H3–H6.
- Link list format — list items in sections should be
- [name](url)with an optional: note. - Absolute URLs, duplicates, plain Markdown and size — relative links break outside your site, HTML means your server returned a web page, and a very large file defeats the purpose of an index.
Common problems it catches
The most frequent failure isn't a formatting mistake — it's a server that answers /llms.txt with the site's HTML homepage or a styled 404 page and a 200 status. Browsers show something, so it looks fine, but a model gets HTML instead of Markdown. The URL check detects this and reports it.
Next come files copied from a template with the placeholders left in, sections that contain prose instead of links, and relative paths like /pricing. When checking by URL the tool also looks for a companion llms-full.txt.
After it passes
A valid file is necessary but not enough. Make sure the pages it links to can be read by AI crawlers — run them through the AI crawler view — and that robots.txt doesn't block the bots that would use them (AI crawler checker). If you don't have a file yet, build one with the llms.txt generator.
FAQ
Questions
Is there an official llms.txt validator?+
The format is a community proposal published at llmstxt.org, not a formal standard, so there is no official validator. This tool checks against the structure the proposal describes and flags the problems that make a file hard to use.
My llms.txt passes. Why don't AI engines cite me?+
Citation depends on much more than llms.txt: whether crawlers can reach and read your pages, whether your content answers the question, and what other sites say about you. Use the AEO checker for the technical side and an AI visibility check to see where you stand.
Can the file be served as text/markdown?+
Yes. text/plain and text/markdown both work. What matters is that the body is Markdown text and the status is 200.
Keep reading
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