The web search tool

Overview

• Built-in tool that allows Claude to search the web for current or specialized information
• Claude decides autonomously whether to use the tool based on the question
• No implementation required—the search runs entirely through Claude

How to Enable Web Search

• Create a web search schema with these required fields:
• type: "web_search_2025_0305"
• name: "web_search"
• max_uses: maximum number of searches Claude can perform (e. g. , 5)
• Include the schema in your request to Claude

Response Structure

The response message contains multiple block types:

• Text blocks: Claude's framing and final answer
• Tool use blocks: Show the exact query Claude used for the search
• Web search tool result blocks: List of pages found, including title and URL
• Citation blocks: Text from sources that support Claude's statements

Constraining Search Results

• Use the allowed_domains field to restrict searches to specific domains
• Example: allowed_domains: ["nih. gov"] ensures Claude only searches government health resources
• Useful for ensuring high-quality, authoritative sources

Rendering Results for Users

• Display all text blocks as plain text
• Highlight web search result blocks and citations in the UI
• Show citations with: domain, page title, URL, and exact cited text
• Helps users understand how Claude sourced its information

Takeaways

• Claude has a built-in web search tool that activates autonomously based on the question—no implementation needed beyond including the search schema in your request
• Enable web search by creating a schema with type: "web_search_2025_0305", name: "web_search", and max_uses to set the search limit
• Use allowed_domains to restrict searches to specific authoritative sources (e. g. , ["nih. gov"] for health information)
• Responses include text blocks, tool use blocks showing the search query, result blocks with pages found, and citation blocks with source text
• Display citations to users with domain, page title, URL, and exact quoted text to show how Claude sourced its information