Design a Well-Specified Tool for an AI Agent

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Design a Well-Specified Tool for an AI Agent
agentsintermediateClaudeGPT
agents/tool-use/function-calling

Write a tool/function definition an LLM agent will actually call correctly — the part most tool-use bugs trace back to.

Prompt
I'm adding a tool to an AI agent. Help me write a well-specified tool definition.

What the tool should do: {{tool_purpose}}
Inputs it needs: {{inputs}}
What it returns: {{return_value}}
Constraints or side effects (destructive? rate-limited? costs money?): {{constraints}}

Give me:
1. A tool name that's unambiguous next to the agent's other tools (avoid vague verbs
   like "process" or "handle").
2. A description written for the model, not for a human reading docs — it should
   state exactly when to call this tool and, just as importantly, when NOT to.
3. A parameter schema with each field's type, whether it's required, and one example
   value — flag any parameter that's ambiguous enough a model could plausibly
   misinterpret its format (date strings, IDs, enums).
4. If the tool is destructive, irreversible, or costs money: the exact confirmation
   step the agent should require before calling it for real.

Point out any part of my inputs above that's too vague for a model to use reliably,
rather than filling the gap with an assumption.

When to use this#

Use this before wiring a new tool into an agent, not after debugging why the agent keeps calling it wrong — most tool-use failures trace back to an ambiguous description or an underspecified parameter, not the model’s reasoning.

Tips#

  • If you have two tools whose descriptions could plausibly overlap in the model’s mind, paste both and ask directly: “would a model be able to reliably tell these apart? If not, how would you rename/redescribe them?”
  • For destructive tools, don’t skip the confirmation step even in a personal/internal project — it’s the single highest-leverage guardrail in agent design.
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