llms.txt validator.
The llms.txt validator checks a pasted file line by line against the format rules of the llmstxt.org proposal and lists its findings.
How to use
- Paste the content of your llms.txt file into the box
- Press Validate
- Findings appear with line numbers — if the file is clean, it says so
The tool runs entirely in your browser — no data is sent, no cookies are written.
The text stays in your browser and is not sent to any server. The tool does not fetch the file from its address — you paste the content yourself.
What it checks
- That the file is plain Markdown, not HTML — a server returning a web page at this address is the most common mistake.
- That the first non-empty line is a first-level heading — the proposal’s only required element — and that there is only one.
- That section headings are second-level.
- That list lines inside sections are links: “- [name](url)” with an optional “: note”.
- That addresses are absolute (starting with https://) and unique.
- That a summary block exists and comes before the sections — a suggestion, not a requirement.
What it does not check
Whether the file is consistent with the pages on your site — whether links open, whether notes summarise the pages correctly — is something this tool cannot know; that is editorial work. The file also has no effect on Google Search: llms.txt is an optional summary.
To create a file from scratch, use the llms.txt generator; for what each of the two files does, see the llms.txt and robots.txt guide.