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 costs 10x more tokens than necessary. This skill covers tool design from schema to error handling.

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. Detailed Guide Read [the detailed guide](references/detailed guide.md) before executing this skill. It retains the complete procedure and reference material. Treat its safety, prerequisites, and validation requirements as mandatory. For focused work, load the relevant sections; for end to end work, read the guide completely. Historical Python SDK sketch Mock only: fixed weather is synthetic, not a current forecast. Pin/verify SDK beta API and an account accessible model before any billed call. Tools need bounded execution/approval policies; the runner does not authorize external effects. When to Use User mentions or implies: agent tool User mentions or implies: function calling User mentions or implies: tool schema User mentions or implies: tool design User mentions or implies: mcp server User mentions or implies: mcp tool User mentions or implies: tool use User mentions or implies: build tool for agent User mentions or implies: define function User mentions or implies: input schema User mentions or implies: tool use User mentions or implies: tool result Limitations Use this skill only when the task clearly matches the scope described above. Do not treat the output as a substitute for environment specific validation, testing, or expert review. Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.

agent-tool-builder