purchase_item

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden. It discloses that the tool 'costs gold/faith immediately,' indicating a resource cost and immediate effect. However, it does not mention potential errors (e.g., insufficient funds) or whether the action is reversible.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is very concise, using a single sentence for the main purpose followed by a bulleted list of parameters. Every sentence is necessary, and the structure is front-loaded with the core functionality. No wasted words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the output schema exists (context signals indicate true), the description does not need to explain return values. It covers the tool's action, parameters, and a useful prerequisite. It lacks error handling or success feedback, but for a straightforward purchase tool, this is adequate.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The description explains all four parameters with clear meanings, data sources (e.g., 'from get_cities output'), and examples. This significantly adds value beyond the schema, which has no descriptions and 0% coverage. The parameter documentation is thorough and actionable.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states 'Purchase a unit or building instantly with gold or faith,' which is a specific verb+resource combination. It clearly distinguishes the tool's purpose from siblings by focusing on instant purchase, and mentions a related tool (get_city_production) for prerequisites.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides guidance on when to use by directing users to get_city_production to see available items. It implies a prerequisite but does not explicitly exclude alternatives like city_action, which could also handle purchases indirectly.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.