チュートリアル：ツール使用エージェントの構築

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チュートリアル: ツール使用エージェントの構築

単一のツール呼び出しから本番環境対応のエージェンティックループまでの段階的なガイド。

このチュートリアルでは、5つの同心円で構成されたカレンダー管理エージェントを構築します。各円は完全に実行可能なプログラムであり、その前の円に正確に1つの概念を追加します。最終的には、エージェンティックループを手書きで実装してから、Tool Runner SDKの抽象化に置き換えます。

例として使用するツールはcreate_calendar_eventです。そのスキーマはネストされたオブジェクト、配列、オプショナルフィールドを使用しているため、単一のフラット文字列ではなく、現実的な入力形状をClaudeがどのように処理するかを確認できます。

すべての円は独立して実行されます。任意の円を新しいファイルにコピーすれば、以前の円のコードなしで実行できます。

円1: 単一ツール、単一ターン

最小限のツール使用プログラム: 1つのツール、1つのユーザーメッセージ、1つのツール呼び出し、1つの結果。コードには詳細なコメントが付いているため、各行をツール使用ライフサイクルにマップできます。

リクエストはユーザーメッセージと一緒にtools配列を送信します。Claudeがツールを呼び出すことを決定すると、レスポンスはstop_reason: "tool_use"と、ツール名、一意のid、構造化されたinputを含むtool_useコンテンツブロックで返されます。コードはツールを実行し、その結果をtool_use_idが呼び出しのidと一致するtool_resultブロックで送り返します。

# Ring 1: Single tool, single turn.
# Source for <CodeSource> in build-a-tool-using-agent.mdx.

import json

import anthropic

# Create a client. It reads ANTHROPIC_API_KEY from the environment.
client = anthropic.Anthropic()

# Define one tool. The input_schema is a JSON Schema object describing
# the arguments Claude should pass when it calls this tool. This schema
# includes nested objects (recurrence), arrays (attendees), and optional
# fields, which is closer to real-world tools than a flat string argument.
tools = [
    {
        "name": "create_calendar_event",
        "description": "Create a calendar event with attendees and optional recurrence.",
        "input_schema": {
            "type": "object",
            "properties": {
                "title": {"type": "string"},
                "start": {"type": "string", "format": "date-time"},
                "end": {"type": "string", "format": "date-time"},
                "attendees": {
                    "type": "array",
                    "items": {"type": "string", "format": "email"},
                },
                "recurrence": {
                    "type": "object",
                    "properties": {
                        "frequency": {"enum": ["daily", "weekly", "monthly"]},
                        "count": {"type": "integer", "minimum": 1},
                    },
                },
            },
            "required": ["title", "start", "end"],
        },
    }
]

# Send the user's request along with the tool definition. Claude decides
# whether to call the tool based on the request and the tool description.
response = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=tools,
    tool_choice={"type": "auto", "disable_parallel_tool_use": True},
    messages=[
        {
            "role": "user",
            "content": "Schedule a 30-minute sync with [email protected] and [email protected] next Monday at 10am.",
        }
    ],
)

# When Claude calls a tool, the response has stop_reason "tool_use"
# and the content array contains a tool_use block alongside any text.
print(f"stop_reason: {response.stop_reason}")

# Find the tool_use block. A response may contain text blocks before the
# tool_use block, so scan the content array rather than assuming position.
tool_use = next(block for block in response.content if block.type == "tool_use")
print(f"Tool: {tool_use.name}")
print(f"Input: {tool_use.input}")

# Execute the tool. In a real system this would call your calendar API.
# Here the result is hardcoded to keep the example self-contained.
result = {"event_id": "evt_123", "status": "created"}

# Send the result back. The tool_result block goes in a user message and
# its tool_use_id must match the id from the tool_use block above. The
# assistant's previous response is included so Claude has the full history.
followup = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=tools,
    tool_choice={"type": "auto", "disable_parallel_tool_use": True},
    messages=[
        {
            "role": "user",
            "content": "Schedule a 30-minute sync with [email protected] and [email protected] next Monday at 10am.",
        },
        {"role": "assistant", "content": response.content},
        {
            "role": "user",
            "content": [
                {
                    "type": "tool_result",
                    "tool_use_id": tool_use.id,
                    "content": json.dumps(result),
                }
            ],
        },
    ],
)

# With the tool result in hand, Claude produces a final natural-language
# answer and stop_reason becomes "end_turn".
print(f"stop_reason: {followup.stop_reason}")
final_text = next(block for block in followup.content if block.type == "text")
print(final_text.text)

期待される出力

Output

stop_reason: tool_use
Tool: create_calendar_event
Input: {'title': 'Sync', 'start': '2026-03-30T10:00:00', 'end': '2026-03-30T10:30:00', 'attendees': ['[email protected]', '[email protected]']}
stop_reason: end_turn
I've scheduled your 30-minute sync with Alice and Bob for next Monday at 10am.

最初のstop_reasonはtool_useです。これはClaudeがカレンダーの結果を待っているためです。結果を送信した後、2番目のstop_reasonはend_turnとなり、コンテンツはユーザー向けの自然言語です。

円2: エージェンティックループ

円1ではClaudeが正確に1回ツールを呼び出すと想定していました。実際のタスクでは複数の呼び出しが必要なことがよくあります。Claudeはイベントを作成し、確認を読み、その後別のイベントを作成するかもしれません。解決策は、stop_reasonが"tool_use"でなくなるまでツールを実行し続け、結果をフィードバックするwhileループです。

もう1つの変更は会話履歴です。各リクエストでmessages配列をゼロから再構築する代わりに、実行中のリストを保持し、それに追加します。すべてのターンで完全な以前のコンテキストが表示されます。

# Ring 2: The agentic loop.
# Source for <CodeSource> in build-a-tool-using-agent.mdx.

import json

import anthropic

client = anthropic.Anthropic()

tools = [
    {
        "name": "create_calendar_event",
        "description": "Create a calendar event with attendees and optional recurrence.",
        "input_schema": {
            "type": "object",
            "properties": {
                "title": {"type": "string"},
                "start": {"type": "string", "format": "date-time"},
                "end": {"type": "string", "format": "date-time"},
                "attendees": {
                    "type": "array",
                    "items": {"type": "string", "format": "email"},
                },
                "recurrence": {
                    "type": "object",
                    "properties": {
                        "frequency": {"enum": ["daily", "weekly", "monthly"]},
                        "count": {"type": "integer", "minimum": 1},
                    },
                },
            },
            "required": ["title", "start", "end"],
        },
    }
]


def run_tool(name, tool_input):
    if name == "create_calendar_event":
        return {"event_id": "evt_123", "status": "created", "title": tool_input["title"]}
    return {"error": f"Unknown tool: {name}"}


# Keep the full conversation history in a list so each turn sees prior context.
messages = [
    {
        "role": "user",
        "content": "Schedule a weekly team standup every Monday at 9am for the next 4 weeks. Invite the whole team: [email protected], [email protected], [email protected].",
    }
]

response = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=tools,
    tool_choice={"type": "auto", "disable_parallel_tool_use": True},
    messages=messages,
)

# Loop until Claude stops asking for tools. Each iteration runs the requested
# tool, appends the result to history, and asks Claude to continue.
while response.stop_reason == "tool_use":
    tool_use = next(block for block in response.content if block.type == "tool_use")
    result = run_tool(tool_use.name, tool_use.input)

    messages.append({"role": "assistant", "content": response.content})
    messages.append(
        {
            "role": "user",
            "content": [
                {
                    "type": "tool_result",
                    "tool_use_id": tool_use.id,
                    "content": json.dumps(result),
                }
            ],
        }
    )

    response = client.messages.create(
        model="claude-opus-4-6",
        max_tokens=1024,
        tools=tools,
        tool_choice={"type": "auto", "disable_parallel_tool_use": True},
        messages=messages,
    )

final_text = next(block for block in response.content if block.type == "text")
print(final_text.text)

期待される出力

Output

I've set up your weekly team standup for the next 4 Mondays at 9am with Alice, Bob, and Carol invited.

ループはClaudeがタスクをどのように分解するかに応じて、1回または複数回実行される可能性があります。コードは事前に知る必要がなくなります。

円3: 複数ツール、並列呼び出し

エージェントは通常、1つの機能だけを持ちません。2番目のツールlist_calendar_eventsを追加して、Claudeが新しいものを作成する前に既存のスケジュールを確認できるようにします。

Claudeが複数の独立したツール呼び出しを行う場合、単一のレスポンスで複数のtool_useブロックを返す可能性があります。ループはそれらすべてを処理し、すべての結果を1つのユーザーメッセージで一緒に送り返す必要があります。最初のものだけでなく、response.content内のすべてのtool_useブロックを反復処理します。

# Ring 3: Multiple tools, parallel calls.
# Source for <CodeSource> in build-a-tool-using-agent.mdx.

import json

import anthropic

client = anthropic.Anthropic()

tools = [
    {
        "name": "create_calendar_event",
        "description": "Create a calendar event with attendees and optional recurrence.",
        "input_schema": {
            "type": "object",
            "properties": {
                "title": {"type": "string"},
                "start": {"type": "string", "format": "date-time"},
                "end": {"type": "string", "format": "date-time"},
                "attendees": {
                    "type": "array",
                    "items": {"type": "string", "format": "email"},
                },
                "recurrence": {
                    "type": "object",
                    "properties": {
                        "frequency": {"enum": ["daily", "weekly", "monthly"]},
                        "count": {"type": "integer", "minimum": 1},
                    },
                },
            },
            "required": ["title", "start", "end"],
        },
    },
    {
        "name": "list_calendar_events",
        "description": "List all calendar events on a given date.",
        "input_schema": {
            "type": "object",
            "properties": {
                "date": {"type": "string", "format": "date"},
            },
            "required": ["date"],
        },
    },
]


def run_tool(name, tool_input):
    if name == "create_calendar_event":
        return {"event_id": "evt_123", "status": "created", "title": tool_input["title"]}
    if name == "list_calendar_events":
        return {"events": [{"title": "Existing meeting", "start": "14:00", "end": "15:00"}]}
    return {"error": f"Unknown tool: {name}"}


messages = [
    {
        "role": "user",
        "content": "Check what I have next Monday, then schedule a planning session that avoids any conflicts.",
    }
]

response = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=tools,
    messages=messages,
)

while response.stop_reason == "tool_use":
    # A single response can contain multiple tool_use blocks. Process all of
    # them and return all results together in one user message.
    tool_results = []
    for block in response.content:
        if block.type == "tool_use":
            result = run_tool(block.name, block.input)
            tool_results.append(
                {
                    "type": "tool_result",
                    "tool_use_id": block.id,
                    "content": json.dumps(result),
                }
            )

    messages.append({"role": "assistant", "content": response.content})
    messages.append({"role": "user", "content": tool_results})

    response = client.messages.create(
        model="claude-opus-4-6",
        max_tokens=1024,
        tools=tools,
        messages=messages,
    )

final_text = next(block for block in response.content if block.type == "text")
print(final_text.text)

期待される出力

Output

I checked your calendar for next Monday and found an existing meeting from 2pm to 3pm. I've scheduled the planning session for 10am to 11am to avoid the conflict.

並列実行と順序保証の詳細については、並列ツール使用を参照してください。

円4: エラーハンドリング

ツールは失敗します。カレンダーAPIが参加者が多すぎるイベントを拒否するか、日付が不正な形式である可能性があります。ツールがエラーを発生させた場合、クラッシュする代わりにis_error: trueでエラーメッセージを送り返します。Claudeはエラーを読み、修正された入力で再試行したり、ユーザーに説明を求めたり、制限事項を説明したりできます。

# Ring 4: Error handling.
# Source for <CodeSource> in build-a-tool-using-agent.mdx.

import json

import anthropic

client = anthropic.Anthropic()

tools = [
    {
        "name": "create_calendar_event",
        "description": "Create a calendar event with attendees and optional recurrence.",
        "input_schema": {
            "type": "object",
            "properties": {
                "title": {"type": "string"},
                "start": {"type": "string", "format": "date-time"},
                "end": {"type": "string", "format": "date-time"},
                "attendees": {
                    "type": "array",
                    "items": {"type": "string", "format": "email"},
                },
                "recurrence": {
                    "type": "object",
                    "properties": {
                        "frequency": {"enum": ["daily", "weekly", "monthly"]},
                        "count": {"type": "integer", "minimum": 1},
                    },
                },
            },
            "required": ["title", "start", "end"],
        },
    },
    {
        "name": "list_calendar_events",
        "description": "List all calendar events on a given date.",
        "input_schema": {
            "type": "object",
            "properties": {
                "date": {"type": "string", "format": "date"},
            },
            "required": ["date"],
        },
    },
]


def run_tool(name, tool_input):
    if name == "create_calendar_event":
        if "attendees" in tool_input and len(tool_input["attendees"]) > 10:
            raise ValueError("Too many attendees (max 10)")
        return {"event_id": "evt_123", "status": "created", "title": tool_input["title"]}
    if name == "list_calendar_events":
        return {"events": [{"title": "Existing meeting", "start": "14:00", "end": "15:00"}]}
    raise ValueError(f"Unknown tool: {name}")


messages = [
    {
        "role": "user",
        "content": "Schedule an all-hands with everyone: " + ", ".join(f"user{i}@example.com" for i in range(15)),
    }
]

response = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=tools,
    messages=messages,
)

while response.stop_reason == "tool_use":
    tool_results = []
    for block in response.content:
        if block.type == "tool_use":
            try:
                result = run_tool(block.name, block.input)
                tool_results.append(
                    {"type": "tool_result", "tool_use_id": block.id, "content": json.dumps(result)}
                )
            except Exception as exc:
                # Signal failure so Claude can retry or ask for clarification.
                tool_results.append(
                    {
                        "type": "tool_result",
                        "tool_use_id": block.id,
                        "content": str(exc),
                        "is_error": True,
                    }
                )

    messages.append({"role": "assistant", "content": response.content})
    messages.append({"role": "user", "content": tool_results})

    response = client.messages.create(
        model="claude-opus-4-6",
        max_tokens=1024,
        tools=tools,
        messages=messages,
    )

final_text = next(block for block in response.content if block.type == "text")
print(final_text.text)

期待される出力

Output

I tried to schedule the all-hands but the calendar only allows 10 attendees per event. I can split this into two sessions, or you can let me know which 10 people to prioritize.

is_errorフラグは成功した結果との唯一の違いです。Claudeはフラグとエラーテキストを見て、それに応じて応答します。完全なエラーハンドリングリファレンスについては、ツール呼び出しの処理を参照してください。

円5: Tool Runner SDKの抽象化

円2から4では、同じループを手書きで実装しました: APIを呼び出し、stop_reasonをチェックし、ツールを実行し、結果を追加し、繰り返します。Tool Runnerはこれをあなたの代わりに行います。各ツールを関数として定義し、リストをtool_runnerに渡し、ループが完了したら最終メッセージを取得します。エラーラッピング、結果フォーマット、会話管理は内部で処理されます。

Python SDKは@beta_toolデコレータを使用して、型ヒントとdocstringからスキーマを推論します。TypeScript SDKはZodスキーマでbetaZodToolを使用します。

Tool RunnerはPython、TypeScript、およびRuby SDKで利用可能です。ShellおよびCLIタブはコードの代わりにメモを表示します。シェルベースのスクリプトの場合は円4のループを保持してください。

# Ring 5: The Tool Runner SDK abstraction.
# Source for <CodeSource> in build-a-tool-using-agent.mdx.

import json

import anthropic
from anthropic import beta_tool

client = anthropic.Anthropic()


@beta_tool
def create_calendar_event(
    title: str,
    start: str,
    end: str,
    attendees: list[str] | None = None,
    recurrence: dict | None = None,
) -> str:
    """Create a calendar event with attendees and optional recurrence.

    Args:
        title: Event title.
        start: Start time in ISO 8601 format.
        end: End time in ISO 8601 format.
        attendees: Email addresses to invite.
        recurrence: Dict with 'frequency' (daily, weekly, monthly) and 'count'.
    """
    if attendees and len(attendees) > 10:
        raise ValueError("Too many attendees (max 10)")
    return json.dumps({"event_id": "evt_123", "status": "created", "title": title})


@beta_tool
def list_calendar_events(date: str) -> str:
    """List all calendar events on a given date.

    Args:
        date: Date in YYYY-MM-DD format.
    """
    return json.dumps({"events": [{"title": "Existing meeting", "start": "14:00", "end": "15:00"}]})


final_message = client.beta.messages.tool_runner(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=[create_calendar_event, list_calendar_events],
    messages=[
        {
            "role": "user",
            "content": "Check what I have next Monday, then schedule a planning session that avoids any conflicts.",
        }
    ],
).until_done()

for block in final_message.content:
    if block.type == "text":
        print(block.text)

期待される出力

Output

I checked your calendar for next Monday and found an existing meeting from 2pm to 3pm. I've scheduled the planning session for 10am to 11am to avoid the conflict.

出力は円3と同じです。違いはコードにあります: 行数が約半分、手動ループなし、スキーマが実装の隣に存在します。

構築したもの

単一のハードコードされたツール呼び出しから始まり、複数のツール、並列呼び出し、エラーを処理する本番環境対応のエージェントで終わり、その後すべてをTool Runnerに折りたたみました。その過程で、ツール使用プロトコルのすべての部分を見ました: tool_useブロック、tool_resultブロック、tool_use_idマッチング、stop_reasonチェック、およびis_errorシグナリング。

次のステップ

スキーマを磨く

スキーマ仕様とベストプラクティス。

Tool Runnerの詳細解説

完全なSDK抽象化リファレンス。

トラブルシューティング

一般的なツール使用エラーを修正します。

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チュートリアル: ツール使用エージェントの構築

単一のツール呼び出しから本番環境対応のエージェンティックループまでの段階的なガイド。

すべての円は独立して実行されます。任意の円を新しいファイルにコピーすれば、以前の円のコードなしで実行できます。

円1: 単一ツール、単一ターン

# Ring 1: Single tool, single turn.
# Source for <CodeSource> in build-a-tool-using-agent.mdx.

import json

import anthropic

# Create a client. It reads ANTHROPIC_API_KEY from the environment.
client = anthropic.Anthropic()

# Define one tool. The input_schema is a JSON Schema object describing
# the arguments Claude should pass when it calls this tool. This schema
# includes nested objects (recurrence), arrays (attendees), and optional
# fields, which is closer to real-world tools than a flat string argument.
tools = [
    {
        "name": "create_calendar_event",
        "description": "Create a calendar event with attendees and optional recurrence.",
        "input_schema": {
            "type": "object",
            "properties": {
                "title": {"type": "string"},
                "start": {"type": "string", "format": "date-time"},
                "end": {"type": "string", "format": "date-time"},
                "attendees": {
                    "type": "array",
                    "items": {"type": "string", "format": "email"},
                },
                "recurrence": {
                    "type": "object",
                    "properties": {
                        "frequency": {"enum": ["daily", "weekly", "monthly"]},
                        "count": {"type": "integer", "minimum": 1},
                    },
                },
            },
            "required": ["title", "start", "end"],
        },
    }
]

# Send the user's request along with the tool definition. Claude decides
# whether to call the tool based on the request and the tool description.
response = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=tools,
    tool_choice={"type": "auto", "disable_parallel_tool_use": True},
    messages=[
        {
            "role": "user",
            "content": "Schedule a 30-minute sync with [email protected] and [email protected] next Monday at 10am.",
        }
    ],
)

# When Claude calls a tool, the response has stop_reason "tool_use"
# and the content array contains a tool_use block alongside any text.
print(f"stop_reason: {response.stop_reason}")

# Find the tool_use block. A response may contain text blocks before the
# tool_use block, so scan the content array rather than assuming position.
tool_use = next(block for block in response.content if block.type == "tool_use")
print(f"Tool: {tool_use.name}")
print(f"Input: {tool_use.input}")

# Execute the tool. In a real system this would call your calendar API.
# Here the result is hardcoded to keep the example self-contained.
result = {"event_id": "evt_123", "status": "created"}

# Send the result back. The tool_result block goes in a user message and
# its tool_use_id must match the id from the tool_use block above. The
# assistant's previous response is included so Claude has the full history.
followup = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=tools,
    tool_choice={"type": "auto", "disable_parallel_tool_use": True},
    messages=[
        {
            "role": "user",
            "content": "Schedule a 30-minute sync with [email protected] and [email protected] next Monday at 10am.",
        },
        {"role": "assistant", "content": response.content},
        {
            "role": "user",
            "content": [
                {
                    "type": "tool_result",
                    "tool_use_id": tool_use.id,
                    "content": json.dumps(result),
                }
            ],
        },
    ],
)

# With the tool result in hand, Claude produces a final natural-language
# answer and stop_reason becomes "end_turn".
print(f"stop_reason: {followup.stop_reason}")
final_text = next(block for block in followup.content if block.type == "text")
print(final_text.text)

期待される出力

Output

stop_reason: tool_use
Tool: create_calendar_event
Input: {'title': 'Sync', 'start': '2026-03-30T10:00:00', 'end': '2026-03-30T10:30:00', 'attendees': ['[email protected]', '[email protected]']}
stop_reason: end_turn
I've scheduled your 30-minute sync with Alice and Bob for next Monday at 10am.

円2: エージェンティックループ

# Ring 2: The agentic loop.
# Source for <CodeSource> in build-a-tool-using-agent.mdx.

import json

import anthropic

client = anthropic.Anthropic()

tools = [
    {
        "name": "create_calendar_event",
        "description": "Create a calendar event with attendees and optional recurrence.",
        "input_schema": {
            "type": "object",
            "properties": {
                "title": {"type": "string"},
                "start": {"type": "string", "format": "date-time"},
                "end": {"type": "string", "format": "date-time"},
                "attendees": {
                    "type": "array",
                    "items": {"type": "string", "format": "email"},
                },
                "recurrence": {
                    "type": "object",
                    "properties": {
                        "frequency": {"enum": ["daily", "weekly", "monthly"]},
                        "count": {"type": "integer", "minimum": 1},
                    },
                },
            },
            "required": ["title", "start", "end"],
        },
    }
]


def run_tool(name, tool_input):
    if name == "create_calendar_event":
        return {"event_id": "evt_123", "status": "created", "title": tool_input["title"]}
    return {"error": f"Unknown tool: {name}"}


# Keep the full conversation history in a list so each turn sees prior context.
messages = [
    {
        "role": "user",
        "content": "Schedule a weekly team standup every Monday at 9am for the next 4 weeks. Invite the whole team: [email protected], [email protected], [email protected].",
    }
]

response = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=tools,
    tool_choice={"type": "auto", "disable_parallel_tool_use": True},
    messages=messages,
)

# Loop until Claude stops asking for tools. Each iteration runs the requested
# tool, appends the result to history, and asks Claude to continue.
while response.stop_reason == "tool_use":
    tool_use = next(block for block in response.content if block.type == "tool_use")
    result = run_tool(tool_use.name, tool_use.input)

    messages.append({"role": "assistant", "content": response.content})
    messages.append(
        {
            "role": "user",
            "content": [
                {
                    "type": "tool_result",
                    "tool_use_id": tool_use.id,
                    "content": json.dumps(result),
                }
            ],
        }
    )

    response = client.messages.create(
        model="claude-opus-4-6",
        max_tokens=1024,
        tools=tools,
        tool_choice={"type": "auto", "disable_parallel_tool_use": True},
        messages=messages,
    )

final_text = next(block for block in response.content if block.type == "text")
print(final_text.text)

期待される出力

Output

I've set up your weekly team standup for the next 4 Mondays at 9am with Alice, Bob, and Carol invited.

ループはClaudeがタスクをどのように分解するかに応じて、1回または複数回実行される可能性があります。コードは事前に知る必要がなくなります。

円3: 複数ツール、並列呼び出し

# Ring 3: Multiple tools, parallel calls.
# Source for <CodeSource> in build-a-tool-using-agent.mdx.

import json

import anthropic

client = anthropic.Anthropic()

tools = [
    {
        "name": "create_calendar_event",
        "description": "Create a calendar event with attendees and optional recurrence.",
        "input_schema": {
            "type": "object",
            "properties": {
                "title": {"type": "string"},
                "start": {"type": "string", "format": "date-time"},
                "end": {"type": "string", "format": "date-time"},
                "attendees": {
                    "type": "array",
                    "items": {"type": "string", "format": "email"},
                },
                "recurrence": {
                    "type": "object",
                    "properties": {
                        "frequency": {"enum": ["daily", "weekly", "monthly"]},
                        "count": {"type": "integer", "minimum": 1},
                    },
                },
            },
            "required": ["title", "start", "end"],
        },
    },
    {
        "name": "list_calendar_events",
        "description": "List all calendar events on a given date.",
        "input_schema": {
            "type": "object",
            "properties": {
                "date": {"type": "string", "format": "date"},
            },
            "required": ["date"],
        },
    },
]


def run_tool(name, tool_input):
    if name == "create_calendar_event":
        return {"event_id": "evt_123", "status": "created", "title": tool_input["title"]}
    if name == "list_calendar_events":
        return {"events": [{"title": "Existing meeting", "start": "14:00", "end": "15:00"}]}
    return {"error": f"Unknown tool: {name}"}


messages = [
    {
        "role": "user",
        "content": "Check what I have next Monday, then schedule a planning session that avoids any conflicts.",
    }
]

response = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=tools,
    messages=messages,
)

while response.stop_reason == "tool_use":
    # A single response can contain multiple tool_use blocks. Process all of
    # them and return all results together in one user message.
    tool_results = []
    for block in response.content:
        if block.type == "tool_use":
            result = run_tool(block.name, block.input)
            tool_results.append(
                {
                    "type": "tool_result",
                    "tool_use_id": block.id,
                    "content": json.dumps(result),
                }
            )

    messages.append({"role": "assistant", "content": response.content})
    messages.append({"role": "user", "content": tool_results})

    response = client.messages.create(
        model="claude-opus-4-6",
        max_tokens=1024,
        tools=tools,
        messages=messages,
    )

final_text = next(block for block in response.content if block.type == "text")
print(final_text.text)

期待される出力

Output

I checked your calendar for next Monday and found an existing meeting from 2pm to 3pm. I've scheduled the planning session for 10am to 11am to avoid the conflict.

並列実行と順序保証の詳細については、並列ツール使用を参照してください。

円4: エラーハンドリング

# Ring 4: Error handling.
# Source for <CodeSource> in build-a-tool-using-agent.mdx.

import json

import anthropic

client = anthropic.Anthropic()

tools = [
    {
        "name": "create_calendar_event",
        "description": "Create a calendar event with attendees and optional recurrence.",
        "input_schema": {
            "type": "object",
            "properties": {
                "title": {"type": "string"},
                "start": {"type": "string", "format": "date-time"},
                "end": {"type": "string", "format": "date-time"},
                "attendees": {
                    "type": "array",
                    "items": {"type": "string", "format": "email"},
                },
                "recurrence": {
                    "type": "object",
                    "properties": {
                        "frequency": {"enum": ["daily", "weekly", "monthly"]},
                        "count": {"type": "integer", "minimum": 1},
                    },
                },
            },
            "required": ["title", "start", "end"],
        },
    },
    {
        "name": "list_calendar_events",
        "description": "List all calendar events on a given date.",
        "input_schema": {
            "type": "object",
            "properties": {
                "date": {"type": "string", "format": "date"},
            },
            "required": ["date"],
        },
    },
]


def run_tool(name, tool_input):
    if name == "create_calendar_event":
        if "attendees" in tool_input and len(tool_input["attendees"]) > 10:
            raise ValueError("Too many attendees (max 10)")
        return {"event_id": "evt_123", "status": "created", "title": tool_input["title"]}
    if name == "list_calendar_events":
        return {"events": [{"title": "Existing meeting", "start": "14:00", "end": "15:00"}]}
    raise ValueError(f"Unknown tool: {name}")


messages = [
    {
        "role": "user",
        "content": "Schedule an all-hands with everyone: " + ", ".join(f"user{i}@example.com" for i in range(15)),
    }
]

response = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=tools,
    messages=messages,
)

while response.stop_reason == "tool_use":
    tool_results = []
    for block in response.content:
        if block.type == "tool_use":
            try:
                result = run_tool(block.name, block.input)
                tool_results.append(
                    {"type": "tool_result", "tool_use_id": block.id, "content": json.dumps(result)}
                )
            except Exception as exc:
                # Signal failure so Claude can retry or ask for clarification.
                tool_results.append(
                    {
                        "type": "tool_result",
                        "tool_use_id": block.id,
                        "content": str(exc),
                        "is_error": True,
                    }
                )

    messages.append({"role": "assistant", "content": response.content})
    messages.append({"role": "user", "content": tool_results})

    response = client.messages.create(
        model="claude-opus-4-6",
        max_tokens=1024,
        tools=tools,
        messages=messages,
    )

final_text = next(block for block in response.content if block.type == "text")
print(final_text.text)

期待される出力

Output

I tried to schedule the all-hands but the calendar only allows 10 attendees per event. I can split this into two sessions, or you can let me know which 10 people to prioritize.

円5: Tool Runner SDKの抽象化

Python SDKは@beta_toolデコレータを使用して、型ヒントとdocstringからスキーマを推論します。TypeScript SDKはZodスキーマでbetaZodToolを使用します。

# Ring 5: The Tool Runner SDK abstraction.
# Source for <CodeSource> in build-a-tool-using-agent.mdx.

import json

import anthropic
from anthropic import beta_tool

client = anthropic.Anthropic()


@beta_tool
def create_calendar_event(
    title: str,
    start: str,
    end: str,
    attendees: list[str] | None = None,
    recurrence: dict | None = None,
) -> str:
    """Create a calendar event with attendees and optional recurrence.

    Args:
        title: Event title.
        start: Start time in ISO 8601 format.
        end: End time in ISO 8601 format.
        attendees: Email addresses to invite.
        recurrence: Dict with 'frequency' (daily, weekly, monthly) and 'count'.
    """
    if attendees and len(attendees) > 10:
        raise ValueError("Too many attendees (max 10)")
    return json.dumps({"event_id": "evt_123", "status": "created", "title": title})


@beta_tool
def list_calendar_events(date: str) -> str:
    """List all calendar events on a given date.

    Args:
        date: Date in YYYY-MM-DD format.
    """
    return json.dumps({"events": [{"title": "Existing meeting", "start": "14:00", "end": "15:00"}]})


final_message = client.beta.messages.tool_runner(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=[create_calendar_event, list_calendar_events],
    messages=[
        {
            "role": "user",
            "content": "Check what I have next Monday, then schedule a planning session that avoids any conflicts.",
        }
    ],
).until_done()

for block in final_message.content:
    if block.type == "text":
        print(block.text)

期待される出力

Output

I checked your calendar for next Monday and found an existing meeting from 2pm to 3pm. I've scheduled the planning session for 10am to 11am to avoid the conflict.

出力は円3と同じです。違いはコードにあります: 行数が約半分、手動ループなし、スキーマが実装の隣に存在します。

構築したもの

次のステップ

スキーマを磨く

スキーマ仕様とベストプラクティス。

Tool Runnerの詳細解説

完全なSDK抽象化リファレンス。

トラブルシューティング

一般的なツール使用エラーを修正します。

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