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Anthropic's Claude Managed Agents web fetch tool now fetches only URLs that have already appeared in the session.
Anthropic's platform release notes for 7 October say the change reduces the risk of data exfiltration; limited-networking environments also apply their allowed hosts to web search and fetch.
Check our sources · 6 facts from 1 sourceAnthropic's Claude Platform release notes for 7 October 2026 say that in Claude Managed Agents the web_fetch tool now fetches only URLs that have already appeared in the session. Such a URL can come from a user message, a web_search result or a page that web_fetch returned earlier. Anthropic says this reduces the risk of data exfiltration.
A URL that appears only in Claude's own output, the agent's system prompt, an attached document, or the output of a tool such as bash, read or an MCP tool does not count, and a web_fetch call for it returns a url_not_in_prior_context error. To let the agent fetch a URL, it must be sent in the text of a user.message event.
The same notes say a cloud environment with limited networking now also applies its allowed_hosts to the web_search and web_fetch tools. A fetch for a host that does not match returns a url_not_allowed error, and web_search omits results from such hosts.
Underlined sentences link to the facts we checked. Dotted words open a short explainer.
Fact 1 of 6 · from Anthropic
In Claude Managed Agents, the web_fetch tool now fetches only URLs that have already appeared in the session, for example in the text of a user message, in a web_search result, or in a page that web_fetch returned earlier.
Fact 2 of 6 · from Anthropic
This reduces the risk of data exfiltration.
Fact 3 of 6 · from Anthropic
A URL that appears only in Claude's own output, the agent's system prompt, an attached document, or the output of a tool such as bash, read, or an MCP tool does not count: a web_fetch call for it returns a url_not_in_prior_context error result to the agent.
Fact 4 of 6 · from Anthropic
To let the agent fetch a URL, send it in the text of a user.message event.
Fact 6 of 6 · from Anthropic
A web_fetch call for a URL on a host that allowed_hosts does not match returns a url_not_allowed error result to the agent. web_search omits results from such hosts.
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Check our sources
Every sentence above is checked against this source.
1 Claude Platform release notes
Open the source archived copy-
Anthropic's Claude Platform release notes list, under October 7, 2026: "In Claude Managed Agents, the web_fetch tool now fetches only URLs that have already appeared in the session, for example in the text of a user message, in a web_search result, or in a page that web_fetch returned earlier."
citeIn Claude Managed Agents, the web_fetch tool now fetches only URLs that have already appeared in the session, for example in the text of a user message, in a web_search result, or in a page that web_fetch returned earlier.
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The release notes say: "This reduces the risk of data exfiltration."
citeThis reduces the risk of data exfiltration.
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The release notes say that "A URL that appears only in Claude's own output, the agent's system prompt, an attached document, or the output of a tool such as bash, read, or an MCP tool does not count: a web_fetch call for it returns a url_not_in_prior_context error result to the agent."
citeA URL that appears only in Claude's own output, the agent's system prompt, an attached document, or the output of a tool such as bash, read, or an MCP tool does not count: a web_fetch call for it returns a url_not_in_prior_context error result to the agent.
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The release notes say: "To let the agent fetch a URL, send it in the text of a user.message event."
citeTo let the agent fetch a URL, send it in the text of a user.message event.
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The release notes say that in Claude Managed Agents, "a cloud environment with limited networking now also applies its allowed_hosts to the web_search and web_fetch tools".
citeIn Claude Managed Agents, a cloud environment with limited networking now also applies its allowed_hosts to the web_search and web_fetch tools.
-
The release notes say that a web_fetch call for a URL on a host that allowed_hosts does not match "returns a url_not_allowed error result to the agent", and that "web_search omits results from such hosts".
citeA web_fetch call for a URL on a host that allowed_hosts does not match returns a url_not_allowed error result to the agent. web_search omits results from such hosts.
Every sentence above is checked against this source. Each fact has its own address you can cite.
Source 1 · Anthropic
Claude Platform release notes
Anthropic's Claude Platform release notes list, under October 7, 2026: "In Claude Managed Agents, the web_fetch tool now fetches only URLs that have already appeared in the session, for example in the text of a user message, in a web_search result, or in a page that web_fetch returned earlier."
In Claude Managed Agents, the web_fetch tool now fetches only URLs that have already appeared in the session, for example in the text of a user message, in a web_search result, or in a page that web_fetch returned earlier.
The release notes say: "This reduces the risk of data exfiltration."
This reduces the risk of data exfiltration.
The release notes say that "A URL that appears only in Claude's own output, the agent's system prompt, an attached document, or the output of a tool such as bash, read, or an MCP tool does not count: a web_fetch call for it returns a url_not_in_prior_context error result to the agent."
A URL that appears only in Claude's own output, the agent's system prompt, an attached document, or the output of a tool such as bash, read, or an MCP tool does not count: a web_fetch call for it returns a url_not_in_prior_context error result to the agent.
Show all 6 factsShow fewer facts
The release notes say: "To let the agent fetch a URL, send it in the text of a user.message event."
To let the agent fetch a URL, send it in the text of a user.message event.
The release notes say that in Claude Managed Agents, "a cloud environment with limited networking now also applies its allowed_hosts to the web_search and web_fetch tools".
In Claude Managed Agents, a cloud environment with limited networking now also applies its allowed_hosts to the web_search and web_fetch tools.
The release notes say that a web_fetch call for a URL on a host that allowed_hosts does not match "returns a url_not_allowed error result to the agent", and that "web_search omits results from such hosts".
A web_fetch call for a URL on a host that allowed_hosts does not match returns a url_not_allowed error result to the agent. web_search omits results from such hosts.
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