Does your site really serve an llms.txt?
We checked all 500 companies in the S&P 500. Plenty of sites answer 200 at /llms.txt and serve a marketing page, a redirect, or nothing at all. This checks what is actually there.
This is a publishing check. It tells you what your server returns at one path. It does not tell you that an AI assistant reads the file, and it does not tell you anything about your search rankings.
How the check works
Five steps, in this order. Each one exists because a real site fooled a simpler version of this check.
Fetch the path
Request https://your-domain/llms.txt, follow redirects, read up to one megabyte, and give up after fifteen seconds.
Reject HTML
Check the content type, then check the first bytes of the body. Some servers label a web page as plain text. A page is not a file.
Watch where you land
Compare the final path with the requested one. A hop from http to https that still ends at /llms.txt is fine. A hop to the homepage is not a file.
Ask for something that cannot exist
Request a randomized path on the same domain. If it returns the same body, the server answers 200 for everything and the file is a mirage.
Keep unknowns unknown
A 403, a timeout, or a server error is reported as inaccessible. Calling those absent would turn our inability to measure into a claim about you.
Five answers, not two
Valid and invalid is the wrong pair of buckets. Here is what we report instead.
- Title and links
- A real text file with a Markdown H1 and at least one Markdown link. Only 54 of the 500 S&P 500 companies cleared this bar.
- Detected, title only
- A real text file with an H1 and no Markdown links. The proposal allows this. It just does not curate anything for a reader.
- Nonstandard
- A real text response with no Markdown H1. The file exists. The shape does not match the proposal.
- No file
- The server answered, and what came back was a redirect, an HTML page, a generic fallback, an empty body, or an honest 404. This is the most common outcome by a wide margin.
- Could not check
- A 403, a timeout, a network failure, or a server error. Your file may well exist. A bot filter in front of it is a finding of its own.
The llms.txt proposal makes the H1 the only required part. Link sections are optional. So a file without links is nonstandard by our threshold, not invalid by the spec.
Where these rules came from
We ran this method across the S&P 500 before turning it into a tool.
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