What is a tool registry and why is it useful?

• A. A log of executed tool calls.
• B. A random list of tools with no metadata.
• C. A cache of user credentials.
• D. A catalog of available tools with metadata that helps the agent discover, reason about, and select tools.

Answer: (D)

A tool registry is a catalog of available tools along with metadata about each tool. This metadata describes what the tool does, its input and output types, any authentication or usage limits, and example payloads. With this information, the agent can discover which tools exist, reason about which one fits a given task, and select the most appropriate tool to call. It also enables safe and effective tool chaining, since the agent can check compatibility and plan multi-step workflows based on clear descriptions of what each tool expects and returns.

For example, if a user asks for weather information, the registry can indicate a weather tool, what location and date inputs it needs, and what format the forecast output will be. The agent can then route the request to that tool and structure the call correctly, or choose another tool if more data is required. This setup makes the system extensible and maintainable—adding a new tool means registering it with its metadata, without changing the agent’s internal logic.

Other options describe a log, an unstructured list, or credentials, none of which provide the organized discovery and decision-making support that a tool registry offers.