Originally published at claudeguide.io/claude-tool-use-advanced

Claude Tool Use: Advanced Patterns for Production

Tool use (function calling) is how you give Claude access to real-world actions — APIs, databases, file systems. The basic pattern is covered in the agent quickstart. This guide covers the advanced cases: parallel calls, forced invocation, error propagation, streaming with tools, and anti-patterns to avoid in 2026.

Parallel tool calls

Claude can call multiple tools in a single response when it determines they can run concurrently. This is the default behavior when multiple tool calls are independent.

Example: Claude is asked "What is the weather in Seoul and Tokyo?"

Claude returns both tool_use blocks in one response content array. You must handle all of them:

python
import asyncio
import anthropic

client = anthropic.Anthropic()

# For parallel execution, gather results concurrently
async def call_tool_async(name: str, input_data: dict) -

Complete, runnable Python and TypeScript code throughout.

[→ Get Agent SDK Cookbook — $49](https://shoutfirst.gumroad.com/l/ogxhmy?utm_source=claudeguide&utm_medium=article&utm_campaign=claude-tool-use-advanced)

*30-day money-back guarantee. Instant download.*