How it works
The checker runs in two panes. The left pane validates the URL you're hosting at - HTTPS, domain root, exact filename, correct host. The right pane parses response headers you paste in - it expects the full headers block from curl -I. Copy the curl command, run it, paste the output, and the tool tells you which headers are wrong.
Why hosting matters
- Location. llms.txt must live at the domain root. A file at /wp-content/llms.txt or /static/llms.txt is invisible to most crawlers.
- Content type. text/plain is the only content-type that every major crawler accepts. text/html gets dropped by GPTBot and ClaudeBot.
- HTTP status. 200 is the only acceptable response. 301/302 redirects are honored by some crawlers but not all.
- No X-Robots-Tag blocks. A stray noindex X-Robots-Tag on your static file handler silently tells crawlers to skip your llms.txt.
Pair with
Confirm the file contents with the LLMs.txt Tester, check accessibility with the Accessibility Checker, and validate syntax with the LLMs.txt Validator. Strategy reading: what is llms.txt.