LLMs.txt Validator
Check an llms.txt against the llmstxt.org spec.
Validate any llms.txt — by URL, paste or file upload — against the llmstxt.org spec: exactly one H1 site name, a recommended summary blockquote, well-formed '## section' link lists, absolute http(s) URLs, no duplicates and only H1/H2 headings. Get a clear pass/fail per rule, a per-link table, and an optional pass that fetches each link through our server to confirm it's reachable. Free.
How to use LLMs.txt Validator
Pick an input mode
Choose how to load your file in this free online llms.txt validator — fetch it by URL, paste the raw contents, or upload a .txt or .md file directly.
Provide the file
Enter a domain or full llms.txt URL, paste your markdown, or drop a file — bare domains automatically resolve to /llms.txt for you.
Enable link checks
Optionally tick 'Also check that links are reachable' so the validator fetches each link through our server to confirm a healthy HTTP status.
Run validation
Click Validate and the llmstxt.org spec checks run instantly in your browser, verifying the H1 site name, summary blockquote, sections, and absolute URLs.
Review the verdict
Read the Valid or Invalid badge with error and warning counts, a per-line spec checklist, and a links table flagging any broken or duplicate entries.
Export the report
Copy or download the full validation report as a text file to share fixes with your team and keep your llms.txt compliant for AI crawlers.
Frequently asked questions
What is an llms.txt validator and what does it check?
An llms.txt validator checks a file against the llmstxt.org spec so AI crawlers can parse it cleanly. This free online llms.txt validator verifies a single H1 site name, the optional summary blockquote, well-formed ## section link lists, absolute http(s) URLs and the use of only H1 and H2 headings.
How do I validate my llms.txt file?
Enter your domain or the full llms.txt URL, paste the file contents, or upload the file, then click Validate. The validator returns a Valid or Invalid verdict with a list of errors and warnings plus a per-line spec checklist you can act on.
What format should a valid llms.txt follow?
A valid llms.txt starts with exactly one H1 like # Site Name, optionally followed by a > summary blockquote, then ## section headings whose items are - [name](url): notes link lists. URLs should be absolute http or https links with no duplicates.
Why does my llms.txt show as an HTML page instead of being validated?
Single-page apps answer unknown paths with their HTML app shell at HTTP 200, so the file only looks like it exists. The validator detects this and reports it; put a real plain-text llms.txt in your public folder or a server route so it returns as text/plain.
Can the validator check that the links in my llms.txt actually work?
Yes. Enable the 'Also check that links are reachable' option and the validator fetches each link through our server (up to 50) to confirm it returns a healthy HTTP status, flagging any broken or unreachable URLs.
Is the H1 site name or the summary blockquote required in llms.txt?
Only the single H1 site name is strictly required. The summary blockquote is recommended right after the H1 and the validator warns if it is missing, but its absence does not make the file invalid.
Is this llms.txt validator free and is my file kept private?
Yes, it is free. The structure checks run entirely in your browser, and only the optional URL fetch and link-reachability pass use our server — your pasted or uploaded llms.txt is not stored.
Related tools — AI · LLMs.txt tools
- LLMs.txt Generator — Crawl your site and build a spec-compliant llms.txt for AI.
- LLMs.txt Checker — Does a domain have an llms.txt? Detect, preview & flag issues.