What is llms.txt and why is it important?

llms.txt is a proposed file placed at the root of a website (/llms.txt) in Markdown format to guide LLMs through the site's most important content in a clear, structured way. It exists because HTML pages are often cluttered with ads, navigation, scripts, or dynamic content. LLMs benefit from curated, plain-text summaries that fit their context window limits.

How do I validate my llms.txt file?

You can validate your llms.txt file using our free online validator. Simply enter your website URL (e.g., example.com/llms.txt) or paste your file content directly into the validator. The tool will check for required elements like H1 headers, blockquote summaries, H2 sections, and valid URL formats.

What's the difference between llms.txt and llms-full.txt?

llms.txt contains structured links to your important pages with descriptions, while llms-full.txt is a companion file that includes full plain-text content of documentation. llms-full.txt is useful when LLMs can ingest large context without navigating individual pages, but may exceed context windows.

Is this llms.txt validator free to use?

Yes! Our llms.txt validator is completely free to use. No registration required, no limits on usage. We're committed to helping the web become more AI-friendly.

What are the common errors in llms.txt files?

Common errors include: missing H1 header, missing blockquote summary, no H2 sections, broken or malformed URLs, duplicate URL entries, incorrect Markdown formatting, and files that are too large (>500KB). Our validator checks for all these issues and provides detailed error messages.

10 Common LLMs.txt Mistakes and How to Fix Them

Heads up! These 10 mistakes account for 95% of llms.txt validation failures. Learn how to avoid them and ensure your file works perfectly with AI systems.

#1: Missing H1 Header

The Problem: Starting your file without a level 1 heading or using the wrong syntax.

❌ Wrong

My Website Documentation
========================

## About Us
- [Home](https://example.com): Welcome page

✅ Correct

# My Website Documentation

> Comprehensive documentation for our platform

## About Us
- [Home](https://example.com): Welcome page

Fix: Always start with exactly one # followed by a space and your site name.

#2: Missing or Malformed Blockquote

The Problem: Skipping the required blockquote summary or using incorrect syntax.

❌ Wrong

# My API Documentation

This is a summary of our API documentation.

## Endpoints
- [Users API](https://api.example.com/users)

✅ Correct

# My API Documentation

> Comprehensive API documentation for developers building integrations with our platform.

## Endpoints
- [Users API](https://api.example.com/users)

Fix: Use > at the start of each summary line. Keep it concise but descriptive.

#3: Using Relative URLs

The Problem: Using relative paths instead of complete URLs.

❌ Wrong

## Documentation
- [Getting Started](/docs/getting-started): Start here
- [API Guide](../api/guide.html): API reference
- [FAQ](faq): Frequently asked questions

✅ Correct

## Documentation
- [Getting Started](https://example.com/docs/getting-started): Start here
- [API Guide](https://example.com/api/guide): API reference
- [FAQ](https://example.com/faq): Frequently asked questions

Fix: Always use complete URLs starting with https:// or http://.

#4: No H2 Sections

The Problem: Missing the required H2 sections to organize your content.

❌ Wrong

# My Website

> Great content for developers

- [Home](https://example.com): Welcome page
- [About](https://example.com/about): About us
- [Contact](https://example.com/contact): Get in touch

✅ Correct

# My Website

> Great content for developers

## Main Pages
- [Home](https://example.com): Welcome page
- [About](https://example.com/about): About us

## Contact
- [Contact](https://example.com/contact): Get in touch

Fix: Group your links under logical H2 sections using ## syntax.

#5: Broken or Invalid URLs

The Problem: Including URLs that don't work or have typos.

Common URL Issues:

• Typos in domain names (exampl.com instead of example.com)
• Missing protocols (example.com/page instead of https://example.com/page)
• Links to development/localhost URLs
• URLs that return 404 or 500 errors
• Password-protected or private URLs

Fix: Test every URL before adding it. Use our validator to check for broken links.

Quick Fix Reference

Mistake	Quick Fix	Example
Missing H1	Add # Title at start	# My Site
No blockquote	Add > summary	> Site description
Relative URLs	Use full https:// URLs	https://example.com
No H2 sections	Group links under ##	## Documentation
Wrong link format	Use [Text](URL): Description	[API](https://...): Guide

Other Common Mistakes

#6: Duplicate URLs

Including the same URL multiple times in different sections.

#7: File Too Large

Creating files larger than 500KB that may exceed AI context limits.

#8: Poor Link Descriptions

Using generic descriptions like "Click here" instead of descriptive text.

#9: Including Login-Required Pages

Linking to pages that require authentication or are behind paywalls.

#10: Inconsistent Formatting

Mixed spacing, inconsistent bullet points, or malformed Markdown.

Prevention Tips

✓
Use our validator: Check your file with our free validator before publishing
✓
Start with examples: Use our templates as a starting point
✓
Test all links: Manually visit every URL to ensure it works
✓
Keep it updated: Review and update your file regularly

Avoid These Mistakes Today

Use our free validator to check your llms.txt file and catch these common mistakes before they affect your AI visibility.

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