Agent Tool Builder Tools are how AI agents interact with the world. A well-designed tool is the difference between an agent that works and one that hallucinates, fails silently, or wastes tokens. This skill covers tool design from schema to error handling. JSON Schema best practices, description writing that actually helps the LLM, validation, and the emerging MCP standard that's becoming the lingua franca for AI tools. Descriptions guide selection, but implementations enforce correctness, authorization and safety. Both require testing; the model may also inspect exposed code/results. Detaile…