llms.txt Validator — check and fix your file

What is llms.txt and why validate it?

llms.txt is a proposed standard by Answer.AI that helps AI assistants discover and use your website content. It's a simple plain-text file, hosted at the root of your domain (e.g., https://yoursite.com/llms.txt), that tells AI models which pages to reference and how to understand your site's structure.

Validating your llms.txt is important because AI assistants are strict parsers. A missing heading, an invalid URL, or incorrect formatting can cause the AI to fail to parse your file entirely — meaning your content becomes invisible to AI-driven discovery. Common issues include missing # title lines, malformed entry syntax (Title: URL: Description), relative URLs instead of absolute HTTPS URLs, and files that are too large for AI context windows.

Running your llms.txt through this validator ensures that AI assistants like Claude, ChatGPT, and custom agents can correctly interpret your content and cite your pages accurately. A valid llms.txt is the difference between being discoverable by AI and being ignored.

llms.txt format specification

The llms.txt format follows a strict markdown-like structure. Every valid llms.txt must conform to these rules:

# Your Site Name
> A brief description of your site (optional, recommended)

## Section Name One
- Page Title: https://example.com/page: Description of what this page covers
- Another Page: https://example.com/other: What this page offers

## Section Name Two
- Blog Post: https://example.com/blog: Summary of the blog content

• The file must start with a # Title line (level-1 heading) — this is the site name
• An optional > Description line follows the title (recommended for AI context)
• Section headings use ## Section Name — at least one section is required
• Each entry is a bullet point: - Title: URL: Description — the title, URL, and description are separated by :
• All URLs must be absolute HTTPS URLs — relative paths are not supported
• Lines starting with # are comments and are ignored by parsers
• Blank lines separate sections for readability
• The file is served as text/plain or text/markdown content type

Common mistakes and how to fix them

Missing or incorrect title heading

Mistake: File doesn't start with # or uses ## Site Name instead of # Site Name.
Fix: Add # Your Site Name as the very first line of your llms.txt. The # must be followed by a space.

No section headings

Mistake: All entries listed without ## section groups.
Fix: Group related links under ## Section Name headings. A good llms.txt has 2–5 sections like Documentation, Blog, Products, or Support.

Wrong entry format

Mistake: Using commas, tabs, or spaces instead of : as delimiters.
Fix: Use - Title: URL: Description exactly. The first colon separates title from URL, the second colon (after URL) separates URL from description.

Relative or non-HTTPS URLs

Mistake: Using /page or http:// URLs.
Fix: Always use absolute https:// URLs. AI assistants need the full URL to access and cite the page.

File too large

Mistake: Including hundreds of pages in a single llms.txt.
Fix: Keep your llms.txt under 100 lines and 50 sections. Focus on the most important pages — AI assistants work better with curated lists of 10–30 entries.

Contains HTML

Mistake: Including HTML tags like <a>, <div>, or <br> in entries.
Fix: llms.txt is plain text — no HTML allowed. Remove all tags and use markdown-style formatting only.

llms.txt best practices

1. Keep it concise — Include only your most important pages. A good llms.txt has 10–30 entries, not hundreds. AI assistants work better with focused, curated lists.
2. Prioritize high-value pages — List pages that provide the most useful information: documentation, guides, product pages, and key blog posts. Skip thin or duplicate content.
3. Use descriptive titles — Each entry's title should clearly describe the page content. "Getting Started Guide" is better than "Page 1." AI uses these titles to decide which pages to cite.
4. Write meaningful descriptions — The description after the URL tells the AI what the page contains. Be specific: "Step-by-step guide to deploying a Node.js app on AWS" instead of "Deployment guide."
5. Update when content changes — Treat llms.txt like sitemap.xml. When you add or remove important pages, update your llms.txt to keep AI assistants pointing to current content.
6. Include multiple sections — Group related pages under section headings. Sections help AI assistants understand the structure of your site at a glance.
7. Test accessibility — Make sure your llms.txt is publicly accessible. Run it through this validator to catch any issues before AI assistants try to read it.

Frequently asked questions

Last updated Jul 2026. Prices and availability verified at time of writing — check provider pages for current rates.