Create Tool

Create Tool

Generate custom tool boilerplate with @tool decorator.

Arguments

• $1: Tool name (snake_case)
• $ARGUMENTS: Tool description and purpose (after name)

Instructions

You are creating a custom tool for use in custom agents.

Step 1: Parse Arguments

Extract:

• Tool name from $1 (required, snake_case)
• Description from remaining arguments

If no name provided, STOP and ask for tool name. If no description provided, STOP and ask for tool purpose.

Step 2: Identify Parameters

Based on the tool purpose, determine:

• What inputs does the tool need?
• Which are required vs optional?
• What types (str, int, float, bool)?

Step 3: Generate Tool Definition

Create tool using @tool decorator:

from typing import Any
from claude_agent_sdk import tool

@tool(
    "[tool_name]",
    "[Description for agent - when to use this tool]",
    {
        "param1": str,
        "param2": int,
    }
)
async def [tool_name](args: dict[str, Any]) -> dict[str, Any]:
    """
    [Brief docstring]
    """
    try:
        # Extract parameters
        param1 = args["param1"]
        param2 = args.get("param2", default_value)

        # Validate inputs
        if not param1:
            return {
                "content": [{"type": "text", "text": "Error: param1 required"}],
                "is_error": True
            }

        # Perform operation
        result = perform_operation(param1, param2)

        # Return success
        return {
            "content": [{"type": "text", "text": str(result)}]
        }

    except Exception as e:
        return {
            "content": [{"type": "text", "text": f"Error: {str(e)}"}],
            "is_error": True
        }

Step 4: Generate MCP Server Setup

from claude_agent_sdk import create_sdk_mcp_server

# Create server with tool
[server_name]_server = create_sdk_mcp_server(
    name="[server_name]",
    version="1.0.0",
    tools=[[tool_name]]
)

Step 5: Generate Agent Configuration

from claude_agent_sdk import ClaudeAgentOptions, ClaudeSDKClient

options = ClaudeAgentOptions(
    mcp_servers={"[server_name]": [server_name]_server},
    allowed_tools=["mcp__[server_name]__[tool_name]"],
    system_prompt=system_prompt,
    model="opus",
)

# IMPORTANT: Use ClaudeSDKClient for custom tools
async with ClaudeSDKClient(options=options) as client:
    await client.query(prompt)
    async for message in client.receive_response():
        pass

Output

## Tool Created

**Name:** [tool_name]
**Server:** [server_name]
**Tool ID:** mcp__[server_name]__[tool_name]

### Tool Definition

```python
[Generated @tool decorated function]

MCP Server

[Generated server setup]

Agent Configuration

[Generated configuration]

Parameters

Usage Example

Agent prompt: "[example prompt that triggers tool]" Expected call: [tool_name](param1="value", param2=10) Expected result: "[expected output]"

Testing

# Test the tool directly
result = await [tool_name]({"param1": "test", "param2": 10})
assert "content" in result
assert not result.get("is_error", False)

Next Steps

1. Add tool to MCP server
2. Configure agent with tool access
3. Test tool in isolation
4. Test tool through agent

Notes

• See @tool-design skill for design workflow
• See @custom-tool-patterns.md for patterns
• CRITICAL: Use ClaudeSDKClient (not query()) for custom tools

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