llms.txt Validator
Validate a site's llms.txt and llms-full.txt against the llmstxt.org format: H1 title, summary, sections and link syntax. Free, or paste a draft to check.
About the llms.txt Validator
llms.txt is a proposed standard (llmstxt.org) for helping AI assistants understand a website: a short Markdown file at /llms.txt that names the site, sums it up in one paragraph and links its most useful pages, optionally with a companion llms-full.txt holding the full text. This validator fetches both files and checks them against the format, line by line.
Features
- Fetches /llms.txt and /llms-full.txt from any site
- Detects catch-all routes that answer with an HTML page
- Checks the H1 title, blockquote summary and ## sections
- Validates every link line: - [Name](URL): notes
- Flags relative URLs and empty sections
- Paste a draft to validate it before you publish
How to Use
- Enter a domain, or switch to “Paste llms.txt” to check a draft.
- Click Validate llms.txt.
- Fix any errors (a missing H1 is the only hard failure).
- Review the linked pages — they should be your most important, up-to-date content.
Frequently Asked Questions
What is llms.txt?
llms.txt is a proposed standard from llmstxt.org: a Markdown file at the root of a website that tells AI assistants what the site is and links its most important pages. It starts with an H1 title, then a one-paragraph blockquote summary, then ## sections of links.
What is the difference between llms.txt and llms-full.txt?
llms.txt is a short index — a summary and links. llms-full.txt is optional and contains the full text of the important pages in one file, so an AI tool can read everything without following links.
Do ChatGPT and Claude use llms.txt?
It is an emerging convention rather than a rule every AI crawler follows today. Some AI tools and coding assistants read it, and it costs little to publish. Make sure your pages are crawlable and readable without JavaScript first — that matters more.
What makes an llms.txt file invalid?
The only hard requirement is the H1 title on the first line. The validator also warns about a missing summary, sections with no links, list items that aren’t in the - [Name](URL): notes form, relative URLs, and a file served as an HTML page by a catch-all route.