Tool description
A tool description is a structured specification of a callable tool's purpose, capabilities, and invocation interface, including its expected inputs.
Build an AI Agent (From Scratch)
A tool definition is a structured declaration of a callable tool's name, description, parameters, types, and required arguments for access by a language model.
- How it is used
- Guides an LLM’s choice of callable tools and the arguments it supplies for a user request.
- How deep it goes
- Works through schema fields, Python-based generation, external execution, and MCP conversion rather than stopping at a definition.
- Examples
- Uses a calculator schema and multiplication trace, a generated web-search definition, and MCP tool discovery.
- What you can do after
- Build it from scratch by declaring a function schema or generating one from Python metadata, then passing it into a tool-calling workflow.
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AI Agents in Action, Second Edition
Tool metadata is descriptive information about a callable tool, including its name, purpose, and parameter schema.
- How it is used
- Guides agents in selecting callable tools and supplying valid parameters without duplicating tool details in general instructions.
- How deep it goes
- Explains metadata fields, disambiguation, and parameter guidance through code examples, but does not descend into model internals.
- Examples
- Uses search tools, a keyword-based retrieval tool, SequentialThinking, and a multi-agent research, planning, and filesystem flow.
- What you can do after
- Apply it via an SDK by writing distinct descriptions, documenting parameters, and moving general tool instructions out of the prompt.
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Related concepts
- tool usageused by · Tool use is an AI system's invocation of external software functions, services, or other capabilities to obtain information or perform actions.
- software artifactkind of · A software artifact is a persistent work product or object produced or maintained during software development or a related workflow.
- toolconfigures · A tool is an instrument or software capability that enables a person or system to perform a task, obtain information, or interact with resources.
- MCP serverused by · An MCP server is software that implements the Model Context Protocol to expose capabilities or information to compatible clients.
- docstringproduced by · A docstring is a string literal associated with a program element that documents its purpose, interface, behavior, or usage for people and tools.
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