Tool use with Claude

Claude is capable of interacting with external client-side tools and functions

How tool use works

1. Provide Claude with tools and a user prompt

2. Claude decides to use a tool

3. Extract tool input, run code, and return results

4. Claude uses tool result to formulate a response

Tools are user-provided

Claude does not have access to any built-in server-side tools.

The computer use (beta) functionality is an exception

How to implement tool use

Choosing a model

Generally, use Claude 3.7 Sonnet, Claude 3.5 Sonnet or Claude 3 Opus for complex tools and ambiguous queries

複数のツールを扱える

Use Claude 3.5 Haiku or Claude 3 Haiku for straightforward tools

引数を忘れるかも

Specifying tools

name

description

input_schema

Tool use system prompt

When you call the Anthropic API with the tools parameter, we construct a special system prompt from the tool definitions, tool configuration, and any user-specified system prompt

code:txt

In this environment you have access to a set of tools you can use to answer the user's question.

{{ FORMATTING INSTRUCTIONS }}

String and scalar parameters should be specified as is, while lists and objects should use JSON format. Note that spaces for string values are not stripped. The output is not expected to be valid XML and is parsed with regular expressions.

Here are the functions available in JSONSchema format:

{{ TOOL DEFINITIONS IN JSON SCHEMA }}

{{ USER SYSTEM PROMPT }}

{{ TOOL CONFIGURATION }}

Best practices for tool definitions

Provide extremely detailed descriptions

Prioritize descriptions over examples

よい例

descriptionが詳しい

input_schemaの引数のdescriptionに例示

The good description clearly explains what the tool does, when to use it, what data it returns, and what the ticker parameter means.

Controlling Claude’s output

Forcing tool use

JSON output

you can use tools anytime you want the model to return JSON output that follows a provided schema.

クライアントサイドの（実際に実行できる）関数でなくてもよい

Chain of thought

Parallel tool use

無効にもできる

Handling tool use and tool result content blocks

When you receive a tool use response, you should:

積ん読

Differences from other APIs

Unlike APIs that separate tool use or use special roles like tool or function, Anthropic’s API integrates tools directly into the user and assistant message structure.

Tool use examples

CoT

JSON mode

Pricing

Tool use system prompt token countで課金される