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For authentication and model list, see Overview.

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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.

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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

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Basic Example

import os
import anthropic

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

# 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)

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More Resources

Tool Use Documentation

Complete guide on defining tools and handling responses