AI crawlers are automated programs that AI companies use to fetch content from websites. That content is used either to train foundation models or to power real-time answers in AI search. There are more than a dozen distinct AI crawlers active on the web today, and each one has its own user agent, its own schedule, and its own purpose - blocking them indiscriminately removes the site from AI visibility entirely.
What are AI crawlers?
An AI crawler is a bot operated by an AI company that fetches web pages and stores their contents for later use by an AI model. Crawlers are a necessary pre-condition for nearly every AI visibility outcome: without crawlers, the AI has no knowledge of the site's contents, and the site can't be retrieved, cited, or recommended.
AI crawlers fall into two broad categories depending on what the fetched content is used for. Training crawlers gather content to add to the corpus used in foundation model pre-training or fine-tuning. Content crawled today may affect model behavior weeks or months later. Search crawlers fetch content for real-time retrieval - when a user asks a question, the AI searches an index that was built by the search crawler and pulls the most relevant pages into the answer.
Most AI companies now run both types. OpenAI, for example, runs GPTBot for training-data collection and OAI-SearchBot for ChatGPT Search. Treating both bots identically in robots.txt conflates two very different use cases. For a deeper walkthrough of each bot and what it does, see the blog post on how to track AI bot activity on your website.
The major AI crawlers
More than 16 distinct AI user agents now crawl the open web. The ones that matter most for AI visibility today:
OpenAI
GPTBot- training-data crawler. Fetches content for ChatGPT model updates. Documented in the OpenAI bots documentation.OAI-SearchBot- search crawler. Indexes content for ChatGPT Search's real-time retrieval layer.
Anthropic
ClaudeBot- Anthropic's primary web crawler for Claude, operating across training and retrieval depending on configuration.
Google-Extended- an opt-out token, not a separate crawler. AddingGoogle-Extendedto robots.txt Disallow rules blocks the content from being used in Gemini training and Google AI Overview generation, while still allowing Googlebot to index for standard search.Googlebot- Google's long-standing search crawler. Relevant because AI Overviews are partly built on Google's search index.
Perplexity
PerplexityBot- Perplexity's crawler. Perplexity cites sources heavily, so crawler access matters disproportionately for Perplexity visibility.
Others
Meta, Microsoft, Apple, Amazon, Bytedance, and several research labs run additional crawlers (Meta-ExternalAgent, CCBot, FacebookBot, Applebot-Extended, and more). The full list changes quarterly as new AI products launch. The AI Bot Access Checker tests against the current list.
How AI crawlers get blocked (often unintentionally)
Most sites that are invisible to AI are invisible by accident, not by design. Three common causes:
Cloudflare's default-block posture
In July 2025, Cloudflare announced that it would block AI crawlers by default for new customers unless they opt in. Millions of sites sitting behind Cloudflare now require explicit permission for AI crawlers to fetch content. Many site owners don't know this applies to them.
Misconfigured robots.txt
A Disallow: / rule that applies to User-agent: * blocks every crawler including AI bots. Less obviously, rules that look like they're limiting only Googlebot sometimes apply to AI crawlers too because of the pattern-matching order in the robots.txt spec. A structured robots.txt that explicitly addresses each AI user agent is safer.
WAF rules and bot managers
Web application firewalls and bot management platforms sometimes flag AI crawlers as suspicious traffic and block them without logging the block. Sites can be crawled successfully by Googlebot but return 403 errors to GPTBot or PerplexityBot - a pattern that's invisible in standard analytics.
How to verify crawler access
Because the default path of a site's AI visibility runs through crawler access, verifying access is the first step in any AEO audit. Three methods:
- Server log analysis - filter by User-Agent for GPTBot, ClaudeBot, PerplexityBot, OAI-SearchBot, Google-Extended. Look for both presence (they're fetching) and status codes (200s vs 403s).
- Automated access checker - the free AI Bot Access Checker simulates each major AI crawler and confirms whether they receive 200 OK responses.
- robots.txt review - inspect the site's
/robots.txtfile and flag any Disallow rules that match AI user agents either directly or via wildcards.
For a broader view of the AI analytics stage of the 5 A's framework, see the AI Analytics platform module - which automates ongoing crawler-access monitoring.
Training crawlers vs search crawlers
Brands often want different answers for "should AI companies train on our content" vs "should AI companies cite our content in search." These are controlled by different user agents.
Common misconceptions
Blocking GPTBot prevents ChatGPT from citing us
Not quite. GPTBot is the training crawler. Blocking it prevents new content from entering future ChatGPT training data, but it does not block OAI-SearchBot, which is what fetches content for ChatGPT Search's real-time answers. If the goal is to remain citable in ChatGPT Search, allow OAI-SearchBot explicitly.
Allowing AI crawlers slows down the site
In practice, AI crawlers respect standard rate limits and don't produce meaningful load on most sites. The volume of AI crawl requests is far lower than Googlebot's. Performance concerns are usually a false constraint.
robots.txt is enforced
robots.txt is an advisory convention, not a technical enforcement mechanism. Well-behaved AI companies respect it; rogue scrapers ignore it. For sites that need enforcement, WAF rules or Cloudflare bot management provide stronger guarantees than robots.txt alone.
Frequently asked questions
#What are AI crawlers in simple terms?
AI crawlers are automated programs operated by AI companies (OpenAI, Anthropic, Google, Perplexity, and others) that visit websites and store what they find. The stored content is later used either to train foundation models or to power real-time answers in AI search. They work like Google's Googlebot, but with different user agents, different schedules, and different downstream uses.
#How do AI crawlers differ from Googlebot?
Technically they use the same HTTP-fetching mechanics, but their purpose and user agents differ. Googlebot fetches pages to index them for Google Search. AI crawlers fetch pages for one of two purposes: training (long-term foundation model updates) or search/retrieval (real-time answer generation). Some bots like GPTBot are training-only; others like OAI-SearchBot are search-only. Treating them identically in robots.txt often produces unintended results.
#Should I block AI crawlers?
Usually no, unless there is a specific reason. Blocking them removes the site from the AI visibility market entirely - no crawling, no retrieval, no citations, no referral traffic. Exceptions: if a site sells gated premium content, if there's a legal or licensing concern, or if the site is a competitor's brand and doesn't want to appear in AI answers. For most brands, the right default is to allow AI search crawlers (OAI-SearchBot, PerplexityBot) and consider blocking AI training crawlers (GPTBot, Google-Extended) separately.
#What is Cloudflare doing with AI crawlers?
As of July 2025, Cloudflare began blocking AI crawlers by default for new customers unless they opt in. The change was announced as 'Content Independence Day' and framed as giving site owners explicit choice over whether AI companies can crawl their content. For sites on Cloudflare, this means the default posture is to be invisible to AI - a site owner has to actively allow AI bots through for their content to be crawled.
#How do I check which AI crawlers are visiting my site?
Two paths. First, analyze server logs - AI crawlers identify themselves in the User-Agent header with names like GPTBot, ClaudeBot, PerplexityBot, etc. Second, use a free AI Bot Access Checker tool that tests whether each major AI crawler can reach the site successfully. AI-Advisors provides both an interactive checker and server-log analysis guidance.
