- Allows Claude to search the web and use the results to inform responses - Provides up-to-date information for current events and recent data - Returns search result information formatted as search result blocks, including links as markdown hyperlinks - Use this tool for accessing information beyond Claude's knowledge cutoff - Searches are performed automatically within a single API call CRITICAL REQUIREMENT - You MUST follow this: - After answering the user's question, you MUST include a "Sources:" section at the end of your response - In the Sources section, list all relevant URLs from the search results as markdown hyperlinks: [Title](URL) - This is MANDATORY - never skip including sources in your response - Example format: [Your answer here] Sources: - [Source Title 1](https://example.com/1) - [Source Title 2](https://example.com/2) Usage notes: - Domain filtering is supported to include or block specific websites - Web search is only available in the US - Account for "Today's date" in . For example, if says "Today's date: 2025-07-01", and the user wants the latest docs, do not use 2024 in the search query. Use 2025.