Llms.txt Validator
Paste any domain and this llms.txt validator fetches its /llms.txt, lints it against the spec, samples the links for 404s and hands you a letter grade with concrete fixes.
How the llms txt checker works
Enter any website URL
Just the domain is enough — the llms txt checker requests /llms.txt directly, exactly like an AI crawler would. That is also how to see the llms.txt file of a website yourself.
We lint the file
The llms.txt validator checks the H1 title, blockquote summary, section structure, link format, content-type and file size against llms.txt best practices.
Read your grade and fix list
You get an A–F grade, every issue ranked by severity, and a sample of linked pages tested for dead URLs.
Why use this llms.txt validator
Catches silent failures
The #1 llms.txt bug: your server returns an HTML fallback page instead of text. This llms txt checker spots it instantly.
Spec-accurate linting
Title, summary, sections, absolute links, descriptions — every rule from the llms.txt spec, checked in order.
Dead-link sampling
A file full of 404s tells AI your site is stale. We fetch a sample of your links and flag every broken one.
A grade you can act on
Not just “valid/invalid” — a score, a letter grade and a prioritized fix list you can hand to a developer.
llms-full.txt aware
We also probe for llms-full.txt, the long-form companion file, and tell you whether it resolves.
See it like an AI sees it
Raw file preview plus a parsed outline — how to validate llm txt file structure without reading Markdown by squint.
Llms.txt best practices worth knowing
How to see the llms.txt file of a website? Append /llms.txt to its domain — for example kairosy.ai/llms.txt — and the file renders as plain text. If you get your homepage or a 404 instead, the site fails the very first check of this llms.txt validator. It is a surprisingly common failure: single-page apps love to swallow unknown paths and return HTML.
The core llms.txt best practices are short: keep the file curated (dozens of links, not thousands), use absolute URLs, give every link a one-line description, serve it as text/plain, and keep it fresh — a stale file with dead links is worse than none. If you are unsure how to validate llm txt file changes after every deploy, bookmark this llms txt checker and re-run it; it takes about five seconds.
What users say about the validator
“Our llms.txt was silently serving the SPA shell for months. This caught it in one run — nothing else did.”
“The letter grade makes it easy to get eng buy-in. “We are a D” lands very differently than “please fix metadata”.”
“Dead-link sampling is the killer feature. Wish it checked every link, but the sample already caught three rotted URLs.”
“I run every prospect’s domain through it before a pitch. Instant conversation starter.”
Llms txt checker FAQs
What does the llms.txt validator actually check?+
Existence (a real 200, not an HTML fallback), content-type, the “# Title” heading, the “> summary” blockquote, “## Section” structure, link format and descriptions, file size, a dead-link sample, and whether llms-full.txt exists.
How to see the llms.txt file of a website without a tool?+
Type the domain followed by /llms.txt into your browser. If it renders as plain Markdown-ish text, it exists; if you see your homepage or an error, it does not.
How to validate llm txt file changes automatically?+
Re-run this validator after each deploy, or add a simple CI step that fetches /llms.txt and fails when the response is HTML or non-200. The grade here maps cleanly to a pass/fail gate.
What are the most important llms.txt best practices?+
Curate rather than dump, use absolute links with one-line descriptions, serve text/plain at the site root, keep it small, and remove dead links promptly. Follow those and you will grade A here.
My file is valid — why is AI still ignoring my site?+
llms.txt helps AI read you; it does not force AI to recommend you. Run a free Kairosy scan to see what ChatGPT, Gemini, Claude and Perplexity actually say about your brand and where the gaps are.
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Fixed the technical bit? Now check what AI says about you
Kairosy asks ChatGPT, Gemini, Claude and Perplexity the questions your buyers ask — and shows whether they recommend you, ignore you, or send buyers to a rival.
Run a free AI brand scan