Intermediate10 min

Anthropic Tool Use & Extended Thinking

Claude's native tool use API: tool definitions, tool_choice modes, extended thinking for complex reasoning, computer use for desktop automation, and streaming with tool calls.

Quick Reference

→Define tools with `input_schema` (JSON Schema) — Claude selects tools based on descriptions and schema
→tool_choice modes: `auto` (model decides), `any` (must use a tool), `tool` (specific tool forced)
→Extended thinking: Claude shows chain-of-thought reasoning before selecting tools — better decisions on complex tasks
→Computer use: Claude interacts with desktop applications via screenshots and coordinate-based actions
→Stream tool use with `stream=True` — handle `content_block_start` and `content_block_delta` events for partial tool inputs

Claude Tool Use Fundamentals

Anthropic's tool use follows a similar pattern to OpenAI but with key differences in structure and capability. Tools are defined with input_schema (not parameters), and Claude's tool selection tends to be more conservative — it explains its reasoning before calling tools, which reduces hallucinated tool calls.

Complete Anthropic tool use with streaming

Tool Choice Modes

Mode	Syntax	Behavior	Use Case
auto	{"type": "auto"}	Model decides whether to use tools or respond directly	General agent — most common mode
any	{"type": "any"}	Model must use at least one tool	Extraction pipelines where tool output is the product
specific tool	{"type": "tool", "name": "search"}	Model must use the named tool	Forcing a search before answering, structured extraction
none (omit tools)	Don't pass tools parameter	Model cannot use tools	Final synthesis step after tool results are collected

Extended Thinking for Complex Tool Selection

Extended thinking lets Claude reason through a problem before acting. For agents, this means better tool selection on ambiguous queries — Claude works through its reasoning in a thinking block, then makes a more informed tool call. This is especially valuable when the agent has many tools and the right choice is not obvious.

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