Is your llms.txt actually valid?
Point the validator at your site to check the file you published, or paste a draft before it goes live. Eleven structural checks against the llmstxt.org format: the required H1 title, the summary blockquote, section structure, link format with line numbers, and size. Paste mode runs entirely in your browser.
URL or paste, same checks
Choose your input
URL mode fetches yoursite.com/llms.txt and confirms the file exists where readers look for it. Paste mode validates a draft without the text ever leaving your browser.
Eleven checks run in order
The one required element first (the H1 title), then the recommended summary, section structure, every link bullet's format with the line numbers of any problems, URL absoluteness, duplicates, and total size.
Fix, re-run, publish
Each failed or warned check says exactly what to change. Pair it with our llms.txt generator if you would rather start from a working file.
What a valid llms.txt looks like
The format is deliberately small: one H1 title as the first line, an optional one-or-two-sentence blockquote summary under it, then H2 sections whose content is markdown link lists in the form of a dash, a bracketed name, and the URL in parentheses, with optional notes after a colon. An Optional section marks links a reader may skip. That is the whole spec, which is exactly why files that deviate from it get skipped by the parsers that do read them.
Why absolute URLs and size both matter
Consumers of these files fetch them without a base URL, so relative links have nothing to resolve against and simply break. Size matters for the same reader: the file is meant to be ingested whole as a compact index. Past roughly twenty thousand characters it stops being an index and starts being a sitemap, and our validator flags it at the same cap our generator enforces.
The honest caveat
No major AI engine currently documents reading llms.txt, and our own testing found no ranking effect from publishing one. It costs little, some crawlers do fetch it, and a valid file is a reasonable low-cost bet on the format's future. But validate it because you chose to publish it, not because it will change this quarter's visibility.
Generator and validator, together
The two tools pair deliberately: generate a file from your site's real pages, paste it here to confirm it survives edits, and re-validate after each content update that adds or removes pages. Files rot when the site moves on; a monthly re-check keeps the index honest.
A valid file is housekeeping. Being cited is the goal.
llms.txt is one small input to how AI systems read your site. Citlyze measures the output: whether ChatGPT, Gemini, and Perplexity actually mention and cite your brand, tracked weekly with the sources behind every answer.
llms.txt validation, answered
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A single H1 title line, first in the file. Everything else, the blockquote summary, the H2 sections, the link lists, is optional structure the format defines on top. A file that is just a title is valid; it just does not tell readers anything.
Does AI recommend you when buyers ask?
Track how ChatGPT, Gemini, Perplexity, DeepSeek, ByteDance, and Grok mention, cite, and rank your brand. Review tracked answers and the gaps to close.
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