claude_tool_web_fetch: Claude web fetch tool

In ellmer: Chat with Large Language Models

Claude web fetch tool

Description

Enables Claude to fetch and analyze content from web URLs. Claude can only fetch URLs that appear in the conversation context (user messages or previous tool results). For security reasons, Claude cannot dynamically construct URLs to fetch.

Requires the web-fetch-2025-09-10 beta header. Learn more in https://docs.claude.com/en/docs/agents-and-tools/tool-use/web-fetch-tool.

Usage

claude_tool_web_fetch(
  max_uses = NULL,
  allowed_domains = NULL,
  blocked_domains = NULL,
  citations = FALSE,
  max_content_tokens = NULL
)

Arguments

max_uses	Integer. Maximum number of fetches allowed per request.
allowed_domains	Character vector. Restrict fetches to specific domains. Cannot be used with blocked_domains.
blocked_domains	Character vector. Exclude specific domains from fetches. Cannot be used with allowed_domains.
citations	Logical. Whether to include citations in the response. Default is TRUE.
max_content_tokens	Integer. Maximum number of tokens to fetch from each URL.

See Also

Other built-in tools: claude_tool_web_search(), google_tool_web_fetch(), google_tool_web_search(), openai_tool_web_search()

Examples

## Not run: 
chat <- chat_claude(beta_headers = "web-fetch-2025-09-10")
chat$register_tool(claude_tool_web_fetch())
chat$chat("What are the latest package releases on https://tidyverse.org/blog")

## End(Not run)

ellmer documentation built on July 14, 2026, 1:07 a.m.