llms.txt Checker: Validate Your File Against the Spec
Check your llms.txt against the llmstxt.org format: H1 title, summary, H2 link sections and working links, with a clear pass, warn or fail for each.
Updated
What the checker tests
It fetches /llms.txt from your site's root (or the exact .txt or .md address you enter) and checks it against the llmstxt.org specification, in the order the spec lays the file out:
- The file exists and is text. A 404, or an HTML page served at that address, fails. A content type other than
text/plainortext/markdownis a warning. - An H1 title on the first line. "The only required section", per the spec. More than one H1 is a warning.
- A blockquote summary (
> ...) right under the title, with the key facts about the site. - H2 sections of link lists. Each item should be a markdown link, optionally followed by a colon and notes. Items that are not links, sections with no links, relative or invalid addresses and duplicates are flagged with their line numbers.
- Links that work. The first 10 links are requested; any that fail or return an error are listed.
- Size. A file over 200 KB is flagged: llms.txt is meant to be a short index, with long text in linked files.
How to read and fix the results
Fail means a tool reading the file would get nothing useful or broken data: fix those first. Warning means the file works but strays from the format or wastes a reader's time. Pass needs nothing.
No file yet, or a messy one? Draft a clean version with the llms.txt generator, edit it, upload it and check again. And keep perspective: llms.txt is optional, and no major AI company has confirmed reading it. Whether AI crawlers can reach your pages at all matters far more; test that with the AI crawler checker.
Common questions
What does a valid llms.txt need?
Only one thing is required by the llmstxt.org format: an H1 line with the name of the site or project. A blockquote summary right after it, and H2 sections holding lists of '- [name](url): notes' links, are what make the file useful.
Why does my llms.txt show as HTML?
Usually the file does not exist and your site returns its normal 'page not found' page with a 200 status, or a plugin serves it through a page template. Upload a real text file to the site root and make sure the server sends it as text/plain or text/markdown.
What is the Optional section in llms.txt?
By convention, an H2 section named 'Optional' holds secondary links that a tool can skip when it needs a shorter context. Put the pages a newcomer must read first in the other sections.
Can I use H3 headings or paragraphs in llms.txt?
Between the summary and the first H2 section the format allows any markdown except headings, such as paragraphs and lists with extra context. Inside the file, keep to one H1 and H2 sections; tools that parse the format may skip or misread deeper headings.
Does a valid llms.txt improve my rankings?
No. Search engines do not use it for ranking, and there is no public evidence that AI assistants use it to choose sources. A valid file simply means that any tool which does read it gets correct, working links.