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. The response includes citations for sources drawn from search results.

The latest web search tool version (web_search_20260209) supports dynamic filtering with Claude Opus 4.6 and Sonnet 4.6. Claude can write and execute code to filter search results before they reach the context window, keeping only relevant information and discarding the rest. This leads to more accurate responses while reducing token consumption. The previous tool version (web_search_20250305) remains available without dynamic filtering.

For Zero Data Retention eligibility and the allowed_callers workaround, see Server tools.

For model support, see the Tool reference.

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.

Dynamic filtering with Opus 4.6 and Sonnet 4.6

Web search is a token-intensive task. With basic web search, Claude needs to pull search results into context, fetch full HTML from multiple websites, and reason over all of it before arriving at an answer. Often, much of this content is irrelevant, which can degrade response quality.

With the web_search_20260209 tool version, Claude can write and execute code to post-process query results. Instead of reasoning over full HTML files, Claude dynamically filters search results before loading them into context, keeping only what's relevant and discarding the rest.

Dynamic filtering is particularly effective for:

• Searching through technical documentation
• Literature review and citation verification
• Technical research
• Response grounding and verification

To enable dynamic filtering, use the web_search_20260209 tool version:

curl https://api.anthropic.com/v1/messages \
    --header "x-api-key: $ANTHROPIC_API_KEY" \
    --header "anthropic-version: 2023-06-01" \
    --header "content-type: application/json" \
    --data '{
        "model": "claude-opus-4-6",
        "max_tokens": 4096,
        "messages": [
            {
                "role": "user",
                "content": "Search for the current prices of AAPL and GOOGL, then calculate which has a better P/E ratio."
            }
        ],
        "tools": [{
            "type": "web_search_20260209",
            "name": "web_search"
        }]
    }'

How to use web search

Provide the web search tool in your API request:

curl https://api.anthropic.com/v1/messages \
    --header "x-api-key: $ANTHROPIC_API_KEY" \
    --header "anthropic-version: 2023-06-01" \
    --header "content-type: application/json" \
    --data '{
        "model": "claude-opus-4-6",
        "max_tokens": 1024,
        "messages": [
            {
                "role": "user",
                "content": "What is the weather in NYC?"
            }
        ],
        "tools": [{
            "type": "web_search_20250305",
            "name": "web_search",
            "max_uses": 5
        }]
    }'

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"
  }
}

Max uses

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

Domain filtering

For domain filtering with allowed_domains and blocked_domains, see Server tools.

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.

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"
}

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

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

The web search citation fields cited_text, title, and url do not count towards input or output token usage.

Errors

When the web search tool encounters an error (such as hitting rate limits), the Claude API still returns a 200 (success) response. The error is represented within the response body using the following structure:

{
  "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

pause_turn stop reason

For continuing after a pause_turn stop reason, see Server tools.

Prompt caching

For caching tool definitions across turns, see Tool use with prompt caching.

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", "partial_json": "{\"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)

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.

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 Claude 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.

Next steps