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Chapter 2 · Domain 1 · 27% of the exam (unconfirmed)

Tool Design Principles

1 min read · Chapter 2 of 4

  • Narrow, well-named tools beat broad ones — a tool called search_orders is easier for a model to use correctly than a generic run_query that accepts arbitrary SQL.
  • Tool descriptions are prompts — the model chooses and calls tools based on the description text, so ambiguous or incomplete descriptions cause wrong tool selection more often than model reasoning failures do.
  • Return structured, bounded output — a tool that dumps an entire database table back to the model wastes context and increases the chance of the model losing track of the actual goal.
  • Fail loudly and specifically — a tool that returns a vague error forces the agent to guess at a fix; a specific error ("order_id not found", not "error") lets the agent self-correct.
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