Web search tool

The web search tool gives Claude direct access to real-time web content, allowing it to answer questions with up-to-date information beyond its knowledge cutoff. Claude automatically cites sources from search results as part of its answer.

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Supported models

Web search is available on:

• Claude 3.7 Sonnet (claude-3-7-sonnet-20250219)
• Claude 3.5 Sonnet (new) (claude-3-5-sonnet-latest)
• Claude 3.5 Haiku (claude-3-5-haiku-latest)

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How web search works

When you add the web search tool to your API request:

1. Claude decides when to search based on the prompt.
2. The API executes the searches and provides Claude with the results. This process may repeat multiple times throughout a single request.
3. At the end of its turn, Claude provides a final response with cited sources.

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How to use web search

Provide the web search tool in your API request:

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Tool definition

The web search tool supports the following parameters:

{
  "type": "web_search_20250305",
  "name": "web_search",

  // Optional: Limit the number of searches per request
  "max_uses": 5,

  // Optional: Only include results from these domains
  "allowed_domains": ["example.com", "trusteddomain.org"],

  // Optional: Never include results from these domains
  "blocked_domains": ["untrustedsource.com"],

  // Optional: Localize search results
  "user_location": {
    "type": "approximate",
    "city": "San Francisco",
    "region": "California",
    "country": "US",
    "timezone": "America/Los_Angeles"
  }
}

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Max uses

The max_uses parameter limits the number of searches performed. If Claude attempts more searches than allowed, the web_search_tool_result will be an error with the max_uses_exceeded error code.

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Domain filtering

When using domain filters:

• Domains should not include the HTTP/HTTPS scheme (use example.com instead of https://example.com)
• Subdomains are automatically included (example.com covers docs.example.com)
• Subpaths are supported (example.com/blog)
• You can use either allowed_domains or blocked_domains, but not both in the same request.

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Localization

The user_location parameter allows you to localize search results based on a user’s location.

• type: The type of location (must be approximate)
• city: The city name
• region: The region or state
• country: The country
• timezone: The IANA timezone ID.

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Response

Here’s an example response structure:

{
  "role": "assistant",
  "content": [
    // 1. Claude's decision to search
    {
      "type": "text",
      "text": "I'll search for when Claude Shannon was born."
    },
    // 2. The search query used
    {
      "type": "server_tool_use",
      "id": "srvtoolu_01WYG3ziw53XMcoyKL4XcZmE",
      "name": "web_search",
      "input": {
        "query": "claude shannon birth date"
      }
    },
    // 3. Search results
    {
      "type": "web_search_tool_result",
      "tool_use_id": "srvtoolu_01WYG3ziw53XMcoyKL4XcZmE",
      "content": [
        {
          "type": "web_search_result",
          "url": "https://en.wikipedia.org/wiki/Claude_Shannon",
          "title": "Claude Shannon - Wikipedia",
          "encrypted_content": "EqgfCioIARgBIiQ3YTAwMjY1Mi1mZjM5LTQ1NGUtODgxNC1kNjNjNTk1ZWI3Y...",
          "page_age": "April 30, 2025"
        }
      ]
    },
    {
      "text": "Based on the search results, ",
      "type": "text"
    },
    // 4. Claude's response with citations
    {
      "text": "Claude Shannon was born on April 30, 1916, in Petoskey, Michigan",
      "type": "text",
      "citations": [
        {
          "type": "web_search_result_location",
          "url": "https://en.wikipedia.org/wiki/Claude_Shannon",
          "title": "Claude Shannon - Wikipedia",
          "encrypted_index": "Eo8BCioIAhgBIiQyYjQ0OWJmZi1lNm..",
          "cited_text": "Claude Elwood Shannon (April 30, 1916 – February 24, 2001) was an American mathematician, electrical engineer, computer scientist, cryptographer and i..."
        }
      ]
    }
  ],
  "id": "msg_a930390d3a",
  "usage": {
    "input_tokens": 6039,
    "output_tokens": 931,
    "server_tool_use": {
      "web_search_requests": 1
    }
  },
  "stop_reason": "end_turn"
}

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Search results

Search results include:

• url: The URL of the source page
• title: The title of the source page
• page_age: When the site was last updated
• encrypted_content: Encrypted content that must be passed back in multi-turn conversations for citations

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Citations

Citations are always enabled for web search, and each web_search_result_location includes:

• url: The URL of the cited source
• title: The title of the cited source
• encrypted_index: A reference that must be passed back for multi-turn conversations.
• cited_text: Up to 150 characters of the cited content

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Errors

If an error occurs during web search, you’ll receive a response that takes the following form:

{
  "type": "web_search_tool_result",
  "tool_use_id": "servertoolu_a93jad",
  "content": {
    "type": "web_search_tool_result_error",
    "error_code": "max_uses_exceeded"
  }
}

These are the possible error codes:

• too_many_requests: Rate limit exceeded
• invalid_input: Invalid search query parameter
• max_uses_exceeded: Maximum web search tool uses exceeded
• query_too_long: Query exceeds maximum length
• unavailable: An internal error occurred

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pause_turn stop reason

The response may include a pause_turn stop reason, which indicates that the API paused a long-running turn. You may provide the response back as-is in a subsequent request to let Claude continue its turn, or modify the content if you wish to interrupt the conversation.

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Prompt caching

Web search works with prompt caching. To enable prompt caching, add at least one cache_control breakpoint in your request. The system will automatically cache up until the last web_search_tool_result block when executing the tool.

For multi-turn conversations, set a cache_control breakpoint on or after the last web_search_tool_result block to reuse cached content.

For example, to use prompt caching with web search for a multi-turn conversation:

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Streaming

With streaming enabled, you’ll receive search events as part of the stream. There will be a pause while the search executes:

event: message_start
data: {"type": "message_start", "message": {"id": "msg_abc123", "type": "message"}}

event: content_block_start
data: {"type": "content_block_start", "index": 0, "content_block": {"type": "text", "text": ""}}

// Claude's decision to search

event: content_block_start
data: {"type": "content_block_start", "index": 1, "content_block": {"type": "server_tool_use", "id": "srvtoolu_xyz789", "name": "web_search"}}

// Search query streamed
event: content_block_delta
data: {"type": "content_block_delta", "index": 1, "delta": {"type": "input_json_delta", "value": "{\"query\":\"latest quantum computing breakthroughs 2025\"}"}}

// Pause while search executes

// Search results streamed
event: content_block_start
data: {"type": "content_block_start", "index": 2, "content_block": {"type": "web_search_tool_result", "tool_use_id": "srvtoolu_xyz789", "content": [{"type": "web_search_result", "title": "Quantum Computing Breakthroughs in 2025", "url": "https://example.com"}]}}

// Claude's response with citations (omitted in this example)

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Batch requests

You can include the web search tool in the Messages Batches API. Web search tool calls through the Messages Batches API are priced the same as those in regular Messages API requests.

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Usage and pricing

Web search usage is charged in addition to token usage:

"usage": {
  "input_tokens": 105,
  "output_tokens": 6039,
  "cache_read_input_tokens": 7123,
  "cache_creation_input_tokens": 7345,
  "server_tool_use": {
    "web_search_requests": 1
  }
}

Web search is available on the Anthropic API for $10 per 1,000 searches, plus standard token costs for search-generated content. Web search results retrieved throughout a conversation are counted as input tokens, in search iterations executed during a single turn and in subsequent conversation turns.

Each web search counts as one use, regardless of the number of results returned. If an error occurs during web search, the web search will not be billed.