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21 March, 2025
Robots.txt for LLMs: Controlling AI Crawlers on Your Site
The New Audience for Your robots.txt File
For decades, robots.txt has been the internet's foundational tool for communicating with web crawlers. Site owners used it to guide search engine bots like Googlebot and Bingbot—telling them what to index and what to leave alone. But in 2024 and beyond, your robots.txt file has a significant new audience: large language model (LLM) crawlers.
Companies like OpenAI, Anthropic, Google DeepMind, Common Crawl, and dozens of others are actively crawling the web to gather training data, power AI search features, and build knowledge bases. Whether you're a blogger, an e-commerce operator, or a B2B software company, AI bots are almost certainly visiting your site—and what you say in your robots.txt matters more than ever.
This guide explains how robots.txt works for LLMs, which AI crawlers you need to know about, how to write effective rules, and what limitations you should be aware of.
How robots.txt Works (A Quick Refresher)
The robots.txt file lives at the root of your domain (e.g., https://yoursite.com/robots.txt). It uses a simple syntax to define which user-agents (bots) can or cannot access specific parts of your site.
A basic example:
User-agent: *
Disallow: /private/
User-agent: Googlebot
Allow: /
The User-agent: * directive applies to all crawlers by default. You can then add specific rules for named bots. The Disallow directive tells crawlers not to fetch matching paths; Allow overrides a Disallow for a subset of pages.
Importantly, robots.txt is a voluntary protocol. Compliant crawlers will honor these rules; non-compliant ones won't. Most major AI companies do respect robots.txt—but not all third-party scrapers do.
Which AI Crawlers Are Visiting Your Site?
Here are the most significant LLM and AI-related crawlers currently active on the web, along with their user-agent strings:
- GPTBot (OpenAI) –
GPTBot - Google-Extended (Google, for AI training) –
Google-Extended - CCBot (Common Crawl, used by many AI orgs) –
CCBot - anthropic-ai (Anthropic/Claude) –
anthropic-ai - Claude-Web (Anthropic browsing) –
ClaudeBot - PerplexityBot (Perplexity AI) –
PerplexityBot - Bytespider (ByteDance/TikTok) –
Bytespider - Applebot-Extended (Apple AI features) –
Applebot-Extended
This list is growing rapidly. New AI products and research labs are launching their own crawlers regularly, making it important to stay current with what's accessing your site.
How to Block AI Crawlers in robots.txt
If you want to prevent LLM companies from crawling your site for training data, you can add specific Disallow rules for known AI bots. Here's a comprehensive example:
User-agent: GPTBot
Disallow: /
User-agent: Google-Extended
Disallow: /
User-agent: CCBot
Disallow: /
User-agent: anthropic-ai
Disallow: /
User-agent: ClaudeBot
Disallow: /
User-agent: PerplexityBot
Disallow: /
User-agent: Bytespider
Disallow: /
User-agent: Applebot-Extended
Disallow: /
The Disallow: / instruction tells each named bot it cannot access any part of your site. This is the most aggressive approach and is appropriate if you don't want your content used for AI training under any circumstances.
Allowing Select AI Crawlers Strategically
Blocking all AI crawlers isn't always the right move. If you want your content to appear in AI-generated answers—on ChatGPT, Perplexity, Google AI Overviews, or similar products—you may want to allow certain crawlers access to specific content while protecting sensitive areas.
For example:
User-agent: GPTBot
Allow: /blog/
Disallow: /members/
Disallow: /checkout/
User-agent: PerplexityBot
Allow: /blog/
Allow: /resources/
Disallow: /
This approach lets AI search products surface your public content (improving your visibility in AI-powered search results) while blocking access to gated content, customer data areas, and proprietary resources.
What robots.txt Can and Cannot Do for LLM Control
It's important to understand the limitations of relying on robots.txt alone for AI crawler control:
What it can do:
- Signal your preferences to well-behaved, compliant crawlers
- Prevent content from being indexed by major AI platforms that respect the protocol
- Reduce crawl load on your servers
- Differentiate your permissions by bot and by URL path
What it cannot do:
- Prevent non-compliant scrapers from accessing your content
- Remove content already crawled and stored before you added the rules
- Guarantee legal protection in all jurisdictions
- Control how AI companies use content that was already indexed
Robots.txt is a starting point, not a complete solution. For comprehensive content protection, you may also want to consider terms of service updates, meta tags like noindex and noai, and emerging standards like llms.txt.
Robots.txt vs. llms.txt: What's the Difference?
A newer standard gaining traction is llms.txt—a file specifically designed to communicate with large language models about your site's content structure and preferences. While robots.txt tells crawlers what they can access, llms.txt is designed to help LLMs understand your content hierarchy, which pages are most important, and how to best represent your site in AI-generated responses.
Think of robots.txt as the access control layer and llms.txt as the content guidance layer. They can and should coexist. Robots.txt controls if a crawler visits; llms.txt guides how an AI should understand and use your content.
Best Practices for Managing AI Crawlers
- Audit your current robots.txt file. Make sure you know what rules are already in place and which crawlers are currently unrestricted.
- Check your server logs. Review which bots are actually visiting your site and how frequently. Tools like Cloudflare, server analytics, or log parsers can help.
- Make a deliberate choice. Decide whether you want AI crawlers to access your content—for training, for AI search visibility, or not at all. There is no universally correct answer; it depends on your business goals.
- Stay updated on new crawlers. The list of active LLM bots changes frequently. Subscribe to resources that track new user-agents and update your file accordingly.
- Test your configuration. Use tools like Google Search Console's robots.txt tester or third-party validators to ensure your file is syntactically correct and behaving as expected.
- Pair with llms.txt for proactive guidance. If you do want AI platforms to represent your brand accurately, consider adding an llms.txt file to guide how LLMs interpret and cite your content.
Conclusion
The rise of LLMs has quietly transformed what it means to manage a web presence. Your robots.txt file—once a simple directive for search engines—now plays a central role in determining how the most powerful AI systems on the planet interact with your content.
Whether you choose to block, allow, or strategically manage AI crawler access, the most important thing is to make that decision deliberately and keep your configuration current. The web's relationship with AI is evolving fast, and proactive content governance is becoming a core part of any serious digital strategy.
Start by checking your robots.txt today. Know who's visiting. And decide, on your own terms, what role AI plays in the future of your content.
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