Tool Creator Skill

This skill provides comprehensive guidance for creating effective tools for the Strands SDK-based agent system. It supports two types of tools: Agent-as-a-Tool (agents wrapped as tools) and Regular Tools (function-based tools).

About Tools in This System

Tools extend agent capabilities by providing:

1. Agent-as-a-Tool: Specialized agents with their own prompts, models, and sub-tools
2. Regular Tools: Direct function execution for system operations, API calls, or data processing

Tool Anatomy

Every tool in src/tools/ consists of:

# Required components
TOOL_SPEC = {
    "name": "tool_name",
    "description": "What the tool does",
    "inputSchema": {"json": {...}}
}

def handle_tool_name(param: Annotated[type, "description"]):
    """Implementation logic"""
    pass

def tool_name(tool: ToolUse, **kwargs: Any) -> ToolResult:
    """Strands SDK tool wrapper"""
    pass

Tool Creation Process

Follow these steps to create a tool. The process supports both full specification upfront and interactive information gathering.

Step 1: Determine Tool Type

Automatic Detection:

• If user mentions "agent tool", "agent-as-a-tool", or describes complex multi-step operations → Agent-as-a-Tool
• If user mentions "simple tool", "regular tool", or describes direct operations → Regular Tool
• If ambiguous → Ask user

Question to ask if ambiguous:

Which type of tool would you like to create?

1. **Agent-as-a-Tool**: A specialized agent with its own prompt, model, and sub-tools (e.g., coder_agent_tool, reporter_agent_tool)
   - Use when: Complex reasoning, multi-step operations, or domain expertise needed

2. **Regular Tool**: A simple function-based tool (e.g., bash_tool, python_repl_tool)
   - Use when: Direct operations like API calls, file operations, or system commands

Step 2: Gather Basic Tool Information

Collect the following information. If user provided some details already, only ask for missing information.

Required for Both Types:

1. Tool Name (if not provided)

   • Question: "What should the tool be named? (Use snake_case, e.g., 'data_analyzer_tool')"
   • Validation: Must end with '_tool', use snake_case

2. Tool Description (if not provided)

   • Question: "What does this tool do? Provide a clear description of its purpose and capabilities."
   • This becomes the tool's description field that helps other agents decide when to use it

3. Input Parameters (if not provided)

   • Question: "What input parameters does this tool need?"
   • For agent tools, typically: task (string describing what to do)
   • For regular tools: specific parameters (e.g., cmd for bash, code for python)

Step 3: Gather Type-Specific Information

For Regular Tools:

Collect these details (skip if already provided):

1. Implementation Logic

   • Question: "What operation should this tool perform? (e.g., execute subprocess, call API, read file)"
   • Common patterns: subprocess execution, HTTP requests, file operations, data transformations

2. Error Handling

   • Question: "What errors should be handled? (Default: try/except with error logging)"

3. External Dependencies (optional)

   • Question: "Does this tool require external libraries? If yes, which ones?"

For Agent-as-a-Tool:

Collect these details (skip if already provided):

1. Agent's Purpose and Role

   • Question: "What is the agent's primary purpose? What role does it play in the system?"
   • This informs the system prompt creation

2. Agent Model Type

   • Question: "Which LLM model should the agent use?"
   • Options:
     • claude-sonnet-3-7 (recommended for most tasks)
     • claude-sonnet-4 (advanced reasoning)
     • claude-sonnet-3-5-v-2 (legacy)

3. Reasoning Capability

   • Question: "Should this agent use extended thinking/reasoning? (True/False)"
   • Default: False
   • Use True for: complex analysis, planning, strategic decisions

4. Prompt Caching

   • Question: "Should prompt caching be enabled? (Recommended: True for agents called frequently)"
   • Default: (True, None)

5. Sub-tools (if not provided)

   • Question: "Which tools should this agent have access to?"
   • Common options: python_repl_tool, bash_tool, file_read
   • Reference existing tools in src/tools/

6. System Prompt Creation

   • IMPORTANT: For system prompt creation, refer to references/system-prompt-guidelines.md
   • If user hasn't provided a system prompt, ask: "Do you want to create a custom system prompt for this agent?"
   • If yes: Use system-prompt-writer guidelines from references to create an effective prompt
   • If no: Create a basic prompt based on the agent's purpose

Step 4: Create the Tool File

Generate the tool file in src/tools/ using the appropriate template:

• Regular Tool: Use templates/regular_tool_template.py
• Agent-as-a-Tool: Use templates/agent_tool_template.py

File Creation Steps:

1. Load the appropriate template
2. Replace template variables with gathered information
3. If creating system prompt:
   • Create prompt file in src/prompts/[tool_name_without_tool].md
   • Follow system-prompt-writer guidelines from references/system-prompt-guidelines.md
   • Use proper template variable escaping (double braces {{}} for code samples)
4. Write the tool file to src/tools/[tool_name].py
5. Inform user of file locations

Step 5: Validation and Next Steps

After creating the tool:

1. Verify File Creation

   • Confirm tool file exists at src/tools/[tool_name].py
   • If agent tool with prompt, confirm prompt file at src/prompts/[name].md

2. Integration Guidance

   • Inform user how to import and use the new tool:

     from src.tools.[tool_name] import [tool_name]
     
     # Use in agent
     agent = strands_utils.get_agent(
         agent_name="example",
         tools=[tool_name, other_tool],
         ...
     )
     

3. Testing Recommendations

   • Suggest testing the tool in isolation
   • For agent tools: Test with sample tasks
   • For regular tools: Test with sample inputs

Key Design Principles

For All Tools

1. Clear Naming: Tool names should be descriptive and end with _tool
2. Comprehensive Descriptions: Description should clearly state what the tool does and when to use it
3. Annotated Parameters: Use Annotated[type, "description"] for all parameters
4. Consistent Error Handling: Return error messages, don't raise exceptions
5. Logging: Use color-coded logging for visibility

For Agent-as-a-Tool

1. Global State Integration: Always access _global_node_states for shared context
2. Streaming Support: Use async streaming pattern with process_streaming_response_yield
3. State Updates: Update clues, history, and messages in shared state
4. Response Format: Use standard response format templates
5. Prompt Templates: Use apply_prompt_template() with proper context variables

For Regular Tools

1. Simplicity: Keep logic straightforward and focused
2. Decorator Usage: Use @log_io decorator for input/output logging
3. Subprocess Safety: Set timeouts and handle errors for subprocess calls
4. Result Formatting: Return results in consistent format (e.g., "cmd||output")

Common Patterns

Pattern 1: Agent Tool with Analysis Capabilities

# Agent for data analysis tasks
- Model: claude-sonnet-3-7
- Reasoning: False
- Tools: [python_repl_tool, bash_tool]
- Purpose: Execute data analysis and calculations

Pattern 2: Agent Tool for Report Generation

# Agent for creating reports
- Model: claude-sonnet-3-7
- Reasoning: False
- Tools: [python_repl_tool, bash_tool, file_read]
- Purpose: Generate formatted reports from analysis results

Pattern 3: Simple Execution Tool

# Tool for direct command execution
- Type: Regular Tool
- Operation: subprocess.run()
- Error Handling: Capture stderr, return error messages

References

• System Prompt Creation: See references/system-prompt-guidelines.md for comprehensive prompt writing guidance
• Template Files: See templates/ for tool code templates
• Example Tools: See references/tool-examples.md for complete real-world examples

Iteration and Improvement

After creating the initial tool:

1. Test with Real Scenarios: Try the tool with actual use cases
2. Gather Feedback: Identify what works and what doesn't
3. Refine Prompts: For agent tools, improve system prompts based on behavior
4. Optimize Parameters: Adjust input schemas if needed
5. Update Documentation: Keep descriptions accurate

The goal is creating effective, reliable tools that seamlessly integrate with the Strands SDK agent system.