llmstxt.org spec · v1

The llms.txt validator
built for modern AI SEO.

Instantly check any website's llms.txt against the official spec. Free, private, spec-accurate.

Free forever No sign-up Spec-accurate

Free llms.txt validator and checker

This free llms.txt validator instantly checks any llms.txt file for compliance with the official llmstxt.org specification. Paste a domain, click validate, and get a full report in under a second — no sign-up, no install. The llms.txt checker verifies Markdown formatting, required H1 title, blockquote summary, H2 sections, and every link inside your file so you can publish with confidence.

An llms.txt file is the emerging standard for making websites readable to Large Language Models such as ChatGPT, Claude, Perplexity, Google Gemini, and Microsoft Copilot. Placed at /llms.txt in your site's root directory, it tells AI crawlers exactly which pages matter — similar in spirit to robots.txt or sitemap.xml, but designed from the ground up for generative AI and answer engines.

What this llms.txt validator checks

Our llms.txt checker runs every file against the full llmstxt.org spec and surfaces errors, warnings, and improvement suggestions with exact line numbers:

  1. Markdown format — confirms your llms.txt file is valid, parseable Markdown.
  2. H1 project title — verifies the required H1 heading with your site or project name.
  3. Blockquote summary — checks for the recommended > summary immediately after the H1.
  4. Project details — validates optional Markdown prose describing what your site is about.
  5. H2 file lists — parses every H2 section and its Markdown link list:
    • Each link should use [name](url): description format.
    • URLs are parsed and checked for structural validity.
  6. Structural issues — catches duplicate H1s, empty sections, and content appearing before the required title.

How to create and publish llms.txt in 4 steps

  1. Write a Markdown file following the llms.txt format (see the template below).
  2. Save it as llms.txt in your website's root — e.g. https://yourdomain.com/llms.txt.
  3. Run it through this llms.txt validator to catch spec violations before you ship.
  4. Keep it updated: revalidate whenever you add key pages, change navigation, or restructure content.

llms.txt template and example

Copy this llms.txt example as a starting point, then validate it with the checker above:

# Your Project Name

> A one-line summary of what your site or product does and who it's for.

Optional longer description in plain Markdown. Explain the value prop, the
audience, and anything an LLM should know before crawling the links below.

## Docs

- [Quickstart](https://example.com/docs/quickstart): 5-minute getting-started guide
- [API reference](https://example.com/docs/api): Complete REST API documentation
- [Examples](https://example.com/docs/examples): Working code samples

## Optional

- [Changelog](https://example.com/changelog): Release notes and version history
- [Blog](https://example.com/blog): Articles, tutorials, and announcements

Why llms.txt matters for AI SEO and GEO

Traditional SEO optimizes for keyword-matching search engines. Generative Engine Optimization (GEO) and Answer Engine Optimization (AEO) optimize for LLMs that read, summarize, and cite your content directly. A valid llms.txt file is the simplest GEO signal you can publish: it gives AI systems a canonical, machine-readable map of your most important pages before they ever crawl the full site.

Control how ChatGPT, Claude, and Perplexity see your site

ChatGPT Search, Claude, Perplexity, Google AI Overviews, Microsoft Copilot, and other AI-powered assistants increasingly cite sources in their answers. If your llms.txt file is missing or invalid, these tools fall back to guessing which pages matter — and often surface the wrong ones. Running your file through this llms.txt validator ensures AI crawlers see exactly the pages you want them to cite.

Faster indexing, cleaner citations

A well-formed llms.txt acts like a curated table of contents for LLMs. Instead of crawling hundreds of pages to understand your site, an AI agent can read a single Markdown file with direct links and descriptions. The result: faster indexing, more accurate citations, and better representation in AI-generated answers.

llms.txt vs robots.txt vs sitemap.xml

robots.txt controls crawler access. sitemap.xml lists every URL for search engine indexing. llms.txt is different: it provides semantic context — human-readable titles and descriptions that help LLMs understand what each page is about, not just that it exists. All three are complementary. This validator focuses exclusively on llms.txt.

Stay compliant as the llms.txt spec evolves

The llms.txt standard is actively evolving at llmstxt.org. Running your file through this llms.txt checker regularly helps catch compatibility issues early and keeps your site optimized for every new AI search engine and LLM-powered tool that adopts the format.

Features of this llms.txt checker

Full spec validation

Validates every rule in the llmstxt.org specification — H1, blockquote summary, H2 sections, and Markdown link lists.

Line-accurate errors

Each error, warning, and info note includes the exact line number so you can fix your llms.txt file in seconds.

Link parsing

The llms.txt validator parses every URL in your file and flags malformed or unreachable link syntax.

Formatted preview

See your llms.txt rendered as styled Markdown — headings, quotes, and links — exactly as an LLM would parse it.

Zero install, zero CORS

Server-side fetch means you can validate any public llms.txt by URL — no browser extensions, no install, no CORS errors.

Free and private

The llms.txt checker is 100% free, requires no sign-up, and uses only privacy-friendly, cookieless analytics.

How to validate llms.txt in 5 steps

  1. 1

    Enter your website URL

    Type any domain (example.com) or a direct URL to your llms.txt file. The validator auto-resolves /llms.txt.

  2. 2

    Click validate

    The llms.txt checker fetches your file server-side and parses it against the llmstxt.org spec in under a second.

  3. 3

    Review validation results

    See the 5-check summary — Markdown format, H1 title, blockquote, project details, file lists — plus detailed pass/fail output.

  4. 4

    Fix errors and warnings

    Each issue links to a specific line number in your llms.txt file. Edit, save, and deploy the fix.

  5. 5

    Revalidate to confirm

    Re-run the llms.txt validator until every check is green. Bookmark this page for future audits.

llms.txt best practices

  • Keep your llms.txt file under 50 KB — LLMs work best with concise, curated link lists.
  • Always include an H1 project name and a one-line blockquote summary.
  • Write descriptive link text — LLMs use it as a hint about each resource's purpose.
  • Place the file at the root of your domain, not in a subdirectory.
  • Revalidate every time you update your site's navigation or launch new pages.
  • Pair llms.txt with a clean sitemap.xml and robots.txt for maximum AI crawler coverage.

llms.txt frequently asked questions

›What is an llms.txt file?

An llms.txt file is a plain-text Markdown document placed at the root of a website (e.g. example.com/llms.txt) that tells Large Language Models which pages matter and what they're about. Defined by the llmstxt.org spec, it includes an H1 project name, a blockquote summary, and H2 sections of curated Markdown links. This llms.txt validator checks every one of those elements.

›How do I create an llms.txt file?

Create a new file named llms.txt, add an H1 with your project name, a blockquote summary, and one or more H2 sections containing Markdown link lists in the format [title](url): description. Save it at your site root and run it through this llms.txt checker to confirm it's spec-compliant before publishing.

›How do I validate an llms.txt file?

Paste your domain or the full URL of your llms.txt file into the validator at the top of this page and click Validate. The llms.txt checker fetches and parses your file server-side, then shows a 5-check summary, detailed validation results, a formatted preview, and line-numbered improvement suggestions.

›Is llms.txt required for SEO?

llms.txt is not required, but it is strongly recommended if you want accurate representation in AI-powered search. As LLM-based tools like ChatGPT Search, Perplexity, Claude, and Google AI Overviews grow, a valid llms.txt file gives you direct control over which pages they surface — the core idea behind Generative Engine Optimization (GEO).

›How is llms.txt different from robots.txt?

robots.txt tells crawlers which URLs they're allowed to access — it's about access control. llms.txt tells LLMs which URLs matter and what they contain — it's about content understanding and semantic context. They solve different problems and work together. This llms.txt validator checks only llms.txt; use a separate robots.txt tester for that file.

›How is llms.txt different from sitemap.xml?

A sitemap.xml lists every URL on your site in machine-readable XML for traditional search engines. An llms.txt file is a curated, human-readable Markdown summary of your most important pages, designed for LLMs. Think of sitemap.xml as the full index and llms.txt as the highlighted table of contents.

›How often should I update my llms.txt file?

Update your llms.txt file whenever you add key pages, change navigation, rename sections, or restructure content. Revalidate with this llms.txt checker after every edit to catch spec violations before they reach production.

›Does this llms.txt validator cost anything?

No. This llms.txt validator is completely free, requires no sign-up, no API key, and no install. It runs on a serverless edge function and uses only privacy-friendly, cookieless Plausible analytics — no personal data, no cross-site tracking.

›Can I validate an llms.txt file that isn't public yet?

This tool fetches llms.txt files by URL, so it needs a publicly reachable URL. If your file is on staging or behind auth, deploy it to a preview URL first, then paste that URL into the validator.

›Which AI crawlers read llms.txt?

Adoption is still early, but llms.txt is designed for any LLM-powered crawler or agent — including OpenAI GPTBot, ChatGPT-User, Anthropic ClaudeBot, PerplexityBot, Google-Extended, and custom retrieval pipelines. Using this llms.txt validator keeps your file compliant for every current and future reader.

Validate your llms.txt file now

Free, instant, spec-compliant. Use this llms.txt validator to make sure ChatGPT, Claude, Perplexity, Gemini, and every future AI search engine see your site the way you want them to.

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