web-search-tool changed

The first capture of this source. The page was already there, and this is what it said.

---
title: Web search tool
url: https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-search-tool
description: Give Claude access to current web content with cited sources, optional dynamic filtering, and domain controls.
---

<Note>
  For how zero data retention (ZDR) applies to this feature, see [API and data retention](https://platform.claude.com/docs/en/manage-claude/api-and-data-retention).
</Note>

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.

With `web_search_20260209` and later versions, Claude can write and run code that filters the search results before they reach the context window (**dynamic filtering**), keeping only relevant information. Dynamic filtering is available with Claude 4.6 and later models and [Claude Mythos Preview](https://anthropic.com/glasswing).

Three versions of the web search tool are available:

* `web_search_20250305`: basic web search
* `web_search_20260209`: adds [dynamic filtering](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-search-tool#dynamic-filtering)
* `web_search_20260318`: adds [response inclusion](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-search-tool#response-inclusion) control for agentic workflows

The examples on this page use `web_search_20250305` for basic search and `web_search_20260318` for dynamic filtering.

<Note>
  For [Claude Mythos Preview](https://anthropic.com/glasswing), web search is supported on the Claude API, Google Cloud, and Microsoft Foundry. Web search is not available for Mythos Preview on Amazon Bedrock or [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws).
</Note>

For web search's Zero Data Retention eligibility and the related `allowed_callers` configuration, see [Server tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/server-tools#zdr-and-allowed-callers).

For model support, see the [Tool reference](https://platform.claude.com/docs/en/agents-and-tools/tool-use/tool-reference).

## How web search works

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

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

### When Claude searches

Claude searches when the request depends on information that is current, changing, or outside its training data:

* Recent events, news, or announcements
* Current prices, rates, scores, or statistics
* Information about specific organizations, people, or products that might have changed
* Explicit requests to search or look something up

Claude answers directly without searching when the request draws on stable knowledge:

* Established facts, math, science fundamentals, or coding concepts
* Creative writing or brainstorming
* Analysis of content already provided in the conversation
* Conversational turns and greetings

Triggering is steerable through your system prompt: you can encourage Claude to search more readily or to prefer answering directly. For a hard constraint, use `max_uses` to cap the number of searches for each request.

### Dynamic filtering

With basic web search, every search result is loaded into Claude's context window, and much of that content can be irrelevant to the request. With `web_search_20260209` or later, Claude instead writes and runs code that filters the results first, so only relevant content reaches the context window. This reduces token use on search-heavy requests.

Dynamic filtering runs web search from inside [code execution](https://platform.claude.com/docs/en/agents-and-tools/tool-use/code-execution-tool): on `web_search_20260209` and later, the tool's `allowed_callers` field defaults to `["code_execution_20260120"]`, and when dynamic filtering runs, the API provisions the code execution it needs for the request automatically. You don't need to add the code execution tool to `tools` yourself. There are no additional charges for code execution calls made this way beyond the standard token costs.

To call web search directly, without dynamic filtering, set `allowed_callers: ["direct"]`. Models that don't support programmatic tool calling require this setting. Without it, the API returns a 400 error that tells you to set it.

<Note>
  The web search tool (with and without dynamic filtering) is available on the Claude API, [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), and [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry). On Microsoft Foundry, web search requires a [Hosted on Anthropic deployment](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry#additional-features-not-supported-when-hosted-on-azure). On Google Cloud, only the basic web search tool (without dynamic filtering) is available. Web search is not available on Amazon Bedrock.
</Note>

The following examples use `web_search_20260318`:

<CodeGroup>
  ```bash cURL
  curl https://api.anthropic.com/v1/messages \
    -H "x-api-key: $ANTHROPIC_API_KEY" \
    -H "anthropic-version: 2023-06-01" \
    -H "content-type: application/json" \
    -d '{
      "model": "claude-opus-5",
      "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_20260318",
        "name": "web_search"
      }]
    }'
  ```

  ```bash CLI
  ant messages create <<'YAML'
  model: claude-opus-5
  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_20260318
      name: web_search
  YAML
  ```

  ```python Python
  client = anthropic.Anthropic()

  response = client.messages.create(
      model="claude-opus-5",
      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_20260318", "name": "web_search"}],
  )
  print(response)
  ```

  ```typescript TypeScript
  const client = new Anthropic();

  const response = await client.messages.create({
    model: "claude-opus-5",
    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_20260318", name: "web_search" }]
  });

  console.log(response);
  ```

  ```csharp C#
  AnthropicClient client = new();

  var parameters = new MessageCreateParams
  {
      Model = Model.ClaudeOpus5,
      MaxTokens = 4096,
      Messages = [new() { Role = Role.User, Content = "Search for the current prices of AAPL and GOOGL, then calculate which has a better P/E ratio." }],
      Tools = [new ToolUnion(new WebSearchTool20260318())]
  };

  var message = await client.Messages.Create(parameters);
  Console.WriteLine(message);
  ```

  ```go Go
  client := anthropic.NewClient()

  response, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
  	Model:     anthropic.ModelClaudeOpus5,
  	MaxTokens: 4096,
  	Messages: []anthropic.MessageParam{
  		anthropic.NewUserMessage(anthropic.NewTextBlock("Search for the current prices of AAPL and GOOGL, then calculate which has a better P/E ratio.")),
  	},
  	Tools: []anthropic.ToolUnionParam{
  		{OfWebSearchTool20260318: &anthropic.WebSearchTool20260318Param{}},
  	},
  })
  if err != nil {
  	log.Fatal(err)
  }
  fmt.Println(response)
  ```

  ```java Java
  import com.anthropic.models.messages.WebSearchTool20260318;

  void main() {
      AnthropicClient client = AnthropicOkHttpClient.fromEnv();

      MessageCreateParams params = MessageCreateParams.builder()
          .model(Model.CLAUDE_OPUS_5)
          .maxTokens(4096L)
          .addUserMessage("Search for the current prices of AAPL and GOOGL, then calculate which has a better P/E ratio.")
          .addTool(WebSearchTool20260318.builder().build())
          .build();

      Message response = client.messages().create(params);
      IO.println(response);
  }
  ```

  ```php PHP
  $client = new Client();

  $message = $client->messages->create(
      maxTokens: 4096,
      messages: [
          ['role' => 'user', 'content' => 'Search for the current prices of AAPL and GOOGL, then calculate which has a better P/E ratio.'],
      ],
      model: 'claude-opus-5',
      tools: [
          [
              'type' => 'web_search_20260318',
              'name' => 'web_search',
          ],
      ],
  );

  echo $message;
  ```

  ```ruby Ruby
  client = Anthropic::Client.new

  message = client.messages.create(
    model: "claude-opus-5",
    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_20260318",
      name: "web_search"
    }]
  )
  puts message
  ```
</CodeGroup>

## How to use web search

<Note>
  Web search is enabled for your organization unless an administrator has disabled it in the [Claude Console](https://platform.claude.com/settings/privacy), where they can also restrict which domains it searches. If it's disabled, a request that includes the tool fails with a 400 `invalid_request_error` that says web search is not enabled, rather than an [error code](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-search-tool#errors) inside a search result.
</Note>

Provide the web search tool in your API request:

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

  ```bash CLI
  ant messages create \
    --model claude-opus-5 \
    --max-tokens 1024 \
    --message '{role: user, content: What is the weather in NYC?}' \
    --tool '{type: web_search_20250305, name: web_search, max_uses: 5}'
  ```

  ```python Python
  client = anthropic.Anthropic()

  response = client.messages.create(
      model="claude-opus-5",
      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)
  ```

  ```typescript TypeScript
  const client = new Anthropic();

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

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