> ## Documentation Index
> Fetch the complete documentation index at: https://docs.pipellm.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Tool Use

> Claude function calling and tool use

For authentication and model list, see [Overview](/api-reference/anthropic/overview).

## What is Tool Use

Tool Use (also called function calling) allows Claude to interact with external tools, APIs, and data sources. Claude doesn't execute tools directly—it generates structured requests that your application executes.

## How It Works

1. **Define tools** with names, descriptions, and input schemas
2. **Claude identifies** when a tool is needed
3. **Claude generates** a tool use request (JSON)
4. **Your app executes** the tool
5. **Return result** to Claude
6. **Claude responds** with the final answer

## Basic Example

<Tabs>
  <Tab title="Python">
    ```python theme={null}
    import os
    import anthropic

    client = anthropic.Anthropic(
      api_key=os.getenv('PIPELLM_API_KEY'),
      base_url='https://api.pipellm.ai'
    )

    # Define tools
    tools = [
      {
        "name": "get_weather",
        "description": "Get the current weather in a location",
        "input_schema": {
          "type": "object",
          "properties": {
            "location": {
              "type": "string",
              "description": "City name, e.g., San Francisco"
            }
          },
          "required": ["location"]
        }
      }
    ]

    # First call - Claude decides to use the tool
    response = client.messages.create(
      model="claude-sonnet-4-5-20250929",
      max_tokens=1024,
      tools=tools,
      messages=[
        {"role": "user", "content": "What's the weather in Tokyo?"}
      ]
    )

    # Check if Claude wants to use a tool
    if response.stop_reason == "tool_use":
      tool_use = next(b for b in response.content if b.type == "tool_use")
      
      # Execute your tool (example)
      tool_result = {"temperature": "22°C", "condition": "Sunny"}
      
      # Return result to Claude
      final_response = client.messages.create(
        model="claude-sonnet-4-5-20250929",
        max_tokens=1024,
        tools=tools,
        messages=[
          {"role": "user", "content": "What's the weather in Tokyo?"},
          {"role": "assistant", "content": response.content},
          {
            "role": "user",
            "content": [
              {
                "type": "tool_result",
                "tool_use_id": tool_use.id,
                "content": str(tool_result)
              }
            ]
          }
        ]
      )
      
      print(final_response.content[0].text)
    ```
  </Tab>

  <Tab title="Node.js">
    ```javascript theme={null}
    import Anthropic from '@anthropic-ai/sdk';

    const client = new Anthropic({
      apiKey: process.env.PIPELLM_API_KEY,
      baseURL: 'https://api.pipellm.ai'
    });

    const tools = [
      {
        name: "get_weather",
        description: "Get the current weather in a location",
        input_schema: {
          type: "object",
          properties: {
            location: {
              type: "string",
              description: "City name, e.g., San Francisco"
            }
          },
          required: ["location"]
        }
      }
    ];

    const response = await client.messages.create({
      model: 'claude-sonnet-4-5-20250929',
      max_tokens: 1024,
      tools: tools,
      messages: [
        { role: 'user', content: "What's the weather in Tokyo?" }
      ]
    });

    if (response.stop_reason === 'tool_use') {
      const toolUse = response.content.find(b => b.type === 'tool_use');
      
      // Execute your tool
      const toolResult = { temperature: "22°C", condition: "Sunny" };
      
      const finalResponse = await client.messages.create({
        model: 'claude-sonnet-4-5-20250929',
        max_tokens: 1024,
        tools: tools,
        messages: [
          { role: 'user', content: "What's the weather in Tokyo?" },
          { role: 'assistant', content: response.content },
          {
            role: 'user',
            content: [
              {
                type: 'tool_result',
                tool_use_id: toolUse.id,
                content: JSON.stringify(toolResult)
              }
            ]
          }
        ]
      });
      
      console.log(finalResponse.content[0].text);
    }
    ```
  </Tab>
</Tabs>

## More Resources

<Card title="Tool Use Documentation" icon="book" href="https://docs.anthropic.com/en/docs/build-with-claude/tool-use">
  Complete guide on defining tools and handling responses
</Card>