Tool Design for Agents

Design every tool as a contract between a deterministic system and a non-deterministic agent. Unlike human-facing APIs, agent-facing tools must make the contract unambiguous through the description alone -- agents infer intent from descriptions and generate calls that must match expected formats. Every ambiguity becomes a potential failure mode that no amount of prompt engineering can fix.

When to Activate

Activate this skill when:

• Creating new tools for agent systems
• Debugging tool-related failures or misuse
• Optimizing existing tool sets for better agent performance
• Designing tool APIs from scratch
• Evaluating third-party tools for agent integration
• Standardizing tool conventions across a codebase

Core Concepts

Design tools around the consolidation principle: if a human engineer cannot definitively say which tool should be used in a given situation, an agent cannot be expected to do better. Reduce the tool set until each tool has one unambiguous purpose, because agents select tools by comparing descriptions and any overlap introduces selection errors.

Treat every tool description as prompt engineering that shapes agent behavior. The description is not documentation for humans -- it is injected into the agent's context and directly steers reasoning. Write descriptions that answer what the tool does, when to use it, and what it returns, because these three questions are exactly what agents evaluate during tool selection.