list_countries

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

With readOnlyHint=true in annotations, the agent knows it is a safe read operation. The description adds no additional behavioral context such as output format, pagination, or caching behavior. It only provides a domain note ('valid ISO codes'), which is semantic rather than behavioral.

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 a single, concise sentence that is front-loaded with the essential info (what it lists and its purpose). Every word earns its place, though it is terse. No redundancy or filler.

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?

For a simple list tool with one optional parameter and no output schema, the description states the subject matter ('country ISO codes') and its domain. However, it does not clarify the exact return structure (e.g., array of strings), which is left to the agent's inference from the name. It is minimally sufficient but lacks some detail.

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 schema includes a thorough description for the only parameter 'raw' (behavior and debugging purpose), achieving 100% coverage. The tool description does not add any information about parameters beyond what the schema already provides, so the baseline score of 3 is appropriate.

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 clearly identifies the resource as 'valid country ISO codes' and specifies its use case 'for addresses/delivery'. Although it lacks an explicit verb like 'list' or 'returns', the name 'list_countries' implies the action. It distinguishes from sibling list tools by focusing on country codes.

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 phrase 'for addresses/delivery' provides implied usage context, suggesting when this tool would be relevant. However, it offers no explicit guidance on when to use this tool versus alternatives or when not to use it. No exclusions or sibling comparisons are presented.

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