Tool Descriptions Drive Selection

When Claude decides which tool to call, it does not pick based on the tool's name. It reads each tool's description and reasons about which one fits the task.

This is the single most important fact in tool design: the description is the primary selection mechanism. A tool named process_refund with a vague description is harder to select correctly than a clearly described tool with an awkward name.

If you want reliable behavior, you invest your effort in writing descriptions — not in clever naming.

Names are short and ambiguous. Consider two tools: search_orders and lookup_order. From names alone, which one finds an order by ID? Which one filters a list by date? You cannot tell, and neither can the model.

The description carries the real meaning:

• What the tool is for (purpose).
• What it returns.
• What inputs it expects, with examples.
• Its edge cases and applicability boundaries.

Name the tool sensibly, but never rely on the name to disambiguate behavior.