Tool Use Patterns

Advanced patterns for Claude's tool use capability.

Agentic Loop

while True:
    response = client.messages.create(
        model="claude-sonnet-4-20250514",
        tools=tools,
        messages=messages
    )

    if response.stop_reason == "end_turn":
        break

    for block in response.content:
        if block.type == "tool_use":
            result = execute_tool(block.name, block.input)
            messages.append({"role": "assistant", "content": response.content})
            messages.append({"role": "user", "content": [
                {"type": "tool_result", "tool_use_id": block.id, "content": str(result)}
            ]})

Error Handling

{"type": "tool_result", "tool_use_id": id, "is_error": true, "content": "File not found"}

Parallel Tool Calls

Claude can request multiple tools in one response. Execute them concurrently and return all results.

Best Practices

• Keep tool descriptions concise but complete
• Include parameter constraints in the schema
• Return structured data from tools when possible
• Use is_error for graceful failure handling