What is llms.txt? A New Standard for AI Content Indexing in 2025

If you’re familiar with robots.txt, the new llms.txt will feel like its AI-native cousin.

As large language models (LLMs) like ChatGPT, Claude, and Perplexity continue crawling the web to provide direct answers, website owners are starting to ask: How can I control how my content is used?

Enter llms.txt — a new emerging standard designed to signal permissions and preferences to AI crawlers.

🧠 What Is llms.txt?

llms.txt is a simple plain-text file you place at the root of your domain (e.g. yourdomain.com/llms.txt). It declares how your site allows or disallows its content to be used by AI models and LLM-based crawlers.

Think of it as a robot.txt for LLMs, focused not on SEO bots like Googlebot, but AI indexers.

Key Goals of llms.txt:

  • Indicate whether your content can be used in AI training or indexing
  • Define licensing or attribution preferences
  • List specific pages or directories to exclude from LLM crawling

🧾 Example of a Basic llms.txt

# Allow Perplexity and ChatGPT to index but not train
User-agent: ChatGPT
Allow: /
Train: no

User-agent: Claude
Allow: /
Train: no

User-agent: *
Disallow: /private/

# You can also add a link to your terms of service or license:
License: https://yourdomain.com/terms
Attribution: required

🧩 Why It Matters in AEO

If you’re practicing Answer Engine Optimization (AEO), llms.txt is your chance to:

  • Explicitly invite (or block) AI crawlers
  • Protect premium or sensitive content
  • Encourage proper attribution when content is quoted in AI answers

And as ChatGPT and Perplexity become default search interfaces, having control over your AI-facing footprint is as important as SEO was in the Google era.

⚙️ Tools and Resources

🧪 Bonus: Monitor LLM Crawler Activity

Check your server logs or use a service like:

Conclusion

As AI-driven search grows, llms.txt is becoming an essential part of your site’s visibility and control strategy. Whether you want to block LLM training, require attribution, or just be indexed properly — this file gives you a voice.

👉 Need help setting up your llms.txt file?
Fill out our quick form and we’ll help you generate one based on your AEO goals.