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 Mythos Preview, Claude Opus 4.7, Claude Opus 4.6, and Claude 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 Claude Mythos Preview, web search is supported on the Claude API, Microsoft Foundry, and Vertex AI. Web search is not available for Mythos Preview on Amazon Bedrock or Claude Platform on AWS.

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:

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

Dynamic filtering

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

Dynamic filtering requires the code execution tool to be enabled. The web search tool (with and without dynamic filtering) is available on the Claude API, Claude Platform on AWS, and Microsoft Foundry. On Vertex AI, only the basic web search tool (without dynamic filtering) is available. Web search is not available on Amazon Bedrock.

To enable dynamic filtering, use the web_search_20260209 tool version:

How to use web search

Your organization's administrator must enable web search in the Claude Console.

Provide the web search tool in your API request:

Tool definition

The web search tool supports the following parameters:

JSON

{
  "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:

Output

{
  "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.

When displaying API outputs directly to end users, citations must be included to the original source. If you are making modifications to API outputs, including by reprocessing and/or combining them with your own material before displaying them to end users, display citations as appropriate based on consultation with your legal team.

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:

Output

{
  "type": "web_search_tool_result",
  "tool_use_id": "srvtoolu_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:

Output

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

Server tools

Shared mechanics for Anthropic-executed tools.

Tool reference

Directory of all Anthropic-provided tools.

client = anthropic.Anthropic()

response = client.messages.create(
    model="claude-opus-4-7",
    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"}],
)
print(response)

client = anthropic.Anthropic()

response = client.messages.create(
    model="claude-opus-4-7",
    max_tokens=1024,
    messages=[{"role": "user", "content": "What's the weather in NYC?"}],
    tools=[{"type": "web_search_20250305", "name": "web_search", "max_uses": 5}],
)
print(response)

How web search works

Dynamic filtering

How to use web search

Tool definition

Max uses

Domain filtering

Localization

Response

Search results

Citations

Errors

pause_turn stop reason

Prompt caching

Streaming

Batch requests

Usage and pricing

Next steps

`pause_turn` stop reason