Tool-Use Schema Design

Tool schemas are prompts. Bad schemas drive bad calls more than bad prompts do.

The model sees your tool definitions as part of its context. A confusing name, an under-described parameter, or an overloaded tool will make the most carefully-prompted agent unreliable.

When to use this skill

• The user is defining tools for a function-calling agent (Claude, GPT, Gemini, Bedrock, MCP server).
• The user reports the model calling tools with wrong arguments, in the wrong order, or not at all.
• The user is exposing an internal API to an LLM and copying the existing signatures.
• The user is adding a new tool to a working agent and the agent regresses.

The five rules