AI crawler · Anthropic · Fetches when a user asks

Claude-User: what it is, its user agent, and how to block it

Claude-User is Anthropic's fetcher for user requests. Fetches a page when someone asks Claude a question that needs it. In our 13 October 2026 study, 174 of 2,332 live top sites with readable robots.txt rules (7.5%) disallow Claude-User. Part of the AI crawler list.

What Claude-User does

Operator: Anthropic. Job: Fetches when a user asks. Obeys robots.txt.

“Claude-User allows site owners to control which sites can be accessed through these user-initiated requests. Disabling Claude-User on your site prevents our system from retrieving your content in response to a user query, which may reduce your site's visibility for user-directed web search.”

Anthropic's Claude-User documentation Published IP ranges (JSON)

Claude-User user agent

robots.txt token: Claude-User (matched case-insensitively).

Anthropic doesn't publish a full user-agent string for Claude-User. Look for Claude-User in the User-Agent header.

robots.txt: allow or block Claude-User

Allow

User-agent: Claude-User
Allow: /

Block

User-agent: Claude-User
Disallow: /

Affects AI answers and citations. Blocking it refuses the fetch Anthropic makes when a user asks its assistant to read your page.

Once a group names Claude-User, it ignores your User-agent: * rules, so copy any paths you still want blocked into it.

How many top sites block Claude-User

Disallow Claude-User in robots.txt

7.5%

174 of 2,332 sites

In our 13 October 2026 study, 174 of 2,332 live top sites with readable robots.txt rules (7.5%) disallow Claude-User.

Sample: Tranco top 5,000, tested once on 13 October 2026 from one Indian fixed-line connection. The robots.txt share counts live sites (home page 2xx) whose rules we could read, as on the AI visibility hub. Method and CSV in the study.

Check your own site

The AI crawler checker reads your robots.txt the way Claude-User does and tests what your firewall returns. To write the rules, use the AI robots.txt generator.

Check your page: free, about 20 seconds, no sign-in

What it checks

robots.txt for Claude-User: Finds the group Claude-User obeys under RFC 9309 and the rule that decides your page.
What your CDN lets through: Requests the page as OAI-SearchBot, PerplexityBot and Claude-SearchBot and compares the answers with a browser request.
Content without JavaScript: AI crawlers don't run JavaScript. The audit checks how much of the page is in the raw HTML.

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Questions

What is Claude-User?+

Claude-User is Anthropic's fetcher for user requests. Fetches a page when someone asks Claude a question that needs it.

What is Claude-User's user agent?+

Anthropic publishes only the token Claude-User. Match on it in the User-Agent header.

How do I block Claude-User?+

Add "User-agent: Claude-User" followed by "Disallow: /" to your robots.txt. Obeys robots.txt, per Anthropic.

Does blocking Claude-User affect AI search citations?+

Blocking it refuses the fetch Anthropic makes when a user asks its assistant to read your page.

How many websites block Claude-User?+