CtrlK
BlogDocsLog inGet started
Tessl Logo

tessl/pypi-anthropic

The official Python library for the anthropic API

—

Pending

Quality

Pending

Does it follow best practices?

Impact

Pending

No eval scenarios have been run

Overview
Eval results
Files

tool-integration.mddocs/common-tasks/

Tool Integration Tasks

Practical patterns for function calling and agentic workflows. For complete reference, see Tools API and Tool Usage Guide.

Quick Start with Tool Decorator

from anthropic import Anthropic, beta_tool

client = Anthropic()

# Define tool with decorator
@beta_tool
def get_weather(location: str, unit: str = "fahrenheit") -> dict:
    """
    Get weather for a location.

    Args:
        location: City and state, e.g. "San Francisco, CA"
        unit: Temperature unit - "celsius" or "fahrenheit"
    """
    # Your implementation here
    return {
        "location": location,
        "temperature": 72,
        "unit": unit,
        "condition": "sunny"
    }

# Auto-execute tools with tool_runner
for message in client.beta.messages.tool_runner(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    tools=[get_weather],
    messages=[{"role": "user", "content": "What's the weather in NYC?"}]
):
    if message.stop_reason == "end_turn":
        print(message.content[0].text)

That's it! The tool_runner automatically:

  • Sends the request to Claude
  • Detects when Claude wants to use a tool
  • Executes the tool function
  • Sends results back to Claude
  • Continues until Claude responds with text

Manual Tool Handling

For more control over the execution flow:

# 1. Define tool manually
tools = [{
    "name": "get_weather",
    "description": "Get weather for a location",
    "input_schema": {
        "type": "object",
        "properties": {
            "location": {"type": "string", "description": "City and state"}
        },
        "required": ["location"]
    }
}]

# 2. Send initial request
message = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    tools=tools,
    messages=[{"role": "user", "content": "What's the weather in SF?"}]
)

# 3. Check if Claude wants to use a tool
if message.stop_reason == "tool_use":
    # Extract tool use
    tool_use = next(block for block in message.content if block.type == "tool_use")
    print(f"Claude wants to use: {tool_use.name}")
    print(f"With params: {tool_use.input}")

    # 4. Execute the tool
    result = get_weather(location=tool_use.input["location"])

    # 5. Send result back to Claude
    final_message = client.messages.create(
        model="claude-sonnet-4-5-20250929",
        max_tokens=1024,
        tools=tools,
        messages=[
            {"role": "user", "content": "What's the weather in SF?"},
            {"role": "assistant", "content": message.content},
            {
                "role": "user",
                "content": [{
                    "type": "tool_result",
                    "tool_use_id": tool_use.id,
                    "content": str(result)
                }]
            }
        ]
    )

    print(final_message.content[0].text)

Multiple Tools

Claude can choose from multiple tools:

@beta_tool
def get_weather(location: str) -> dict:
    """Get current weather for a location"""
    return {"temp": 72, "condition": "sunny"}

@beta_tool
def search_database(query: str, limit: int = 10) -> list:
    """Search database for items matching query"""
    return [{"id": 1, "name": "Item 1"}, {"id": 2, "name": "Item 2"}]

@beta_tool
def send_email(to: str, subject: str, body: str) -> dict:
    """Send an email"""
    return {"status": "sent", "message_id": "abc123"}

# Claude picks the right tool(s)
for message in client.beta.messages.tool_runner(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    tools=[get_weather, search_database, send_email],
    messages=[{"role": "user", "content": "Check the weather in NYC and email it to bob@example.com"}]
):
    if message.stop_reason == "end_turn":
        print(message.content[0].text)

Async Tools

For I/O-bound operations:

import httpx
from anthropic import AsyncAnthropic, beta_async_tool

client = AsyncAnthropic()

@beta_async_tool
async def fetch_url(url: str) -> str:
    """Fetch content from a URL"""
    async with httpx.AsyncClient() as http_client:
        response = await http_client.get(url)
        return response.text

# Use with async tool_runner
async for message in client.beta.messages.tool_runner(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    tools=[fetch_url],
    messages=[{"role": "user", "content": "Fetch https://example.com and summarize it"}]
):
    if message.stop_reason == "end_turn":
        print(message.content[0].text)

Control Tool Selection

Force Tool Use

Require Claude to use at least one tool:

message = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    tools=[...],
    tool_choice={"type": "any"},  # Force any tool
    messages=[{"role": "user", "content": "Hello"}]
)

Force Specific Tool

Require Claude to use a specific tool:

message = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    tools=[...],
    tool_choice={"type": "tool", "name": "get_weather"},  # Force specific tool
    messages=[{"role": "user", "content": "Hello"}]
)

Disable Tools for a Turn

Temporarily disable tool use:

message = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    tools=[...],
    tool_choice={"type": "none"},  # No tools this turn
    messages=[...]
)

Disable Parallel Tool Use

Force sequential tool calls:

message = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    tools=[...],
    tool_choice={
        "type": "auto",
        "disable_parallel_tool_use": True
    },
    messages=[{"role": "user", "content": "Do task A and then task B"}]
)

Error Handling in Tools

Report tool execution failures to Claude:

@beta_tool
def divide(a: float, b: float) -> float:
    """Divide two numbers"""
    if b == 0:
        raise ValueError("Cannot divide by zero")
    return a / b

# Manual handling with error reporting
message = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    tools=[divide.to_param()],
    messages=[{"role": "user", "content": "What is 10 divided by 0?"}]
)

tool_use = next(block for block in message.content if block.type == "tool_use")

# Execute and catch errors
try:
    result = divide(**tool_use.input)
    tool_result = str(result)
    is_error = False
except Exception as e:
    tool_result = str(e)
    is_error = True

# Send error back to Claude
final_message = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    tools=[divide.to_param()],
    messages=[
        {"role": "user", "content": "What is 10 divided by 0?"},
        {"role": "assistant", "content": message.content},
        {
            "role": "user",
            "content": [{
                "type": "tool_result",
                "tool_use_id": tool_use.id,
                "content": tool_result,
                "is_error": is_error  # Tell Claude this is an error
            }]
        }
    ]
)

print(final_message.content[0].text)  # Claude handles the error gracefully

Stateful Tools

Tools that maintain state:

class Calculator:
    def __init__(self):
        self.memory = 0

    @beta_tool
    def calculate(self, expression: str) -> float:
        """Evaluate a mathematical expression and store result"""
        result = eval(expression)  # Use safe evaluation in production
        self.memory = result
        return result

    @beta_tool
    def recall(self) -> float:
        """Recall the last calculation result"""
        return self.memory

    @beta_tool
    def clear(self) -> str:
        """Clear calculator memory"""
        self.memory = 0
        return "Memory cleared"

# Use stateful tools
calc = Calculator()

for message in client.beta.messages.tool_runner(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    tools=[calc.calculate, calc.recall, calc.clear],
    messages=[{"role": "user", "content": "Calculate 5 * 8, then add 10 to that result"}]
):
    if message.stop_reason == "end_turn":
        print(message.content[0].text)
        print(f"Final memory: {calc.memory}")

Validate Tool Inputs

@beta_tool
def set_temperature(degrees: float, unit: str = "celsius") -> dict:
    """Set thermostat temperature"""
    # Validate unit
    if unit not in ["celsius", "fahrenheit"]:
        raise ValueError(f"Invalid unit: {unit}. Must be 'celsius' or 'fahrenheit'")

    # Validate range
    if degrees < -50 or degrees > 50:
        raise ValueError(f"Temperature {degrees} out of safe range (-50 to 50)")

    # Set temperature
    return {"status": "success", "temperature": degrees, "unit": unit}

Return Structured Data

from typing import TypedDict

class UserInfo(TypedDict):
    id: str
    name: str
    email: str
    created_at: str

@beta_tool
def get_user_info(user_id: str) -> UserInfo:
    """Get user information by ID"""
    # Fetch from database
    return {
        "id": user_id,
        "name": "Alice Smith",
        "email": "alice@example.com",
        "created_at": "2024-01-15"
    }

# Claude can work with structured data
for message in client.beta.messages.tool_runner(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    tools=[get_user_info],
    messages=[{"role": "user", "content": "Get info for user user_123 and send them a welcome email"}]
):
    if message.stop_reason == "end_turn":
        print(message.content[0].text)

Complex Tool Example

Database query tool with validation:

@beta_tool
def query_database(
    table: str,
    filters: dict,
    limit: int = 10,
    sort_by: str | None = None
) -> list[dict]:
    """
    Query database with filters.

    Args:
        table: Table name to query
        filters: Key-value pairs for filtering (e.g., {"status": "active"})
        limit: Maximum number of results (1-100)
        sort_by: Optional field to sort by
    """
    # Validate inputs
    valid_tables = ["users", "orders", "products"]
    if table not in valid_tables:
        raise ValueError(f"Invalid table. Must be one of: {valid_tables}")

    if not 1 <= limit <= 100:
        raise ValueError("Limit must be between 1 and 100")

    # Execute query (pseudocode)
    results = db.query(table).filter(**filters).limit(limit)
    if sort_by:
        results = results.sort(sort_by)

    return results.all()

Tool Usage Best Practices

1. Clear Descriptions

Write clear docstrings - Claude uses these to decide when to call the tool:

@beta_tool
def search_products(
    query: str,
    category: str | None = None,
    min_price: float | None = None,
    max_price: float | None = None,
    in_stock_only: bool = True
) -> list[dict]:
    """
    Search product catalog for matching items.

    Use this tool when the user wants to find or browse products.

    Args:
        query: Search keywords or product name
        category: Optional category filter (e.g., "electronics", "books", "clothing")
        min_price: Minimum price in USD
        max_price: Maximum price in USD
        in_stock_only: Only show products currently in stock
    """
    ...

2. Use Type Hints

Type hints improve schema generation:

from typing import Literal

@beta_tool
def book_appointment(
    date: str,  # Use specific format hints in docstring
    time: str,
    service: Literal["haircut", "coloring", "styling"]
) -> dict:
    """
    Book an appointment.

    Args:
        date: Date in YYYY-MM-DD format
        time: Time in HH:MM format (24-hour)
        service: Type of service
    """
    ...

3. Return Useful Data

Return structured data that Claude can work with:

@beta_tool
def get_order_status(order_id: str) -> dict:
    """Get status of an order"""
    return {
        "order_id": order_id,
        "status": "shipped",
        "tracking_number": "1Z999AA10123456784",
        "estimated_delivery": "2024-01-20",
        "items_count": 3
    }

See Also

Install with Tessl CLI

npx tessl i tessl/pypi-anthropic

docs

common-tasks

basic-messaging.md

multimodal-input.md

streaming-responses.md

tool-integration.md

index.md

tile.json