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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description restates 'Side effects: none (read-only)', which adds no new information and is redundant. It is consistent but does not go beyond annotations to describe behavioral nuances like auth requirements or response format.

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 brief, with the purpose statement front-loaded. However, the second sentence about 'Side effects: none (read-only)' duplicates information already available in annotations, making it slightly redundant. The overall length is appropriate but could be tightened.

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?

The tool is simple with one parameter and an output schema, so the description's scope is sufficient. It does not need to detail return values since an output schema exists. The only minor gap is a lack of explicit guidance on when to use this tool versus siblings, but the purpose is clear enough for correct invocation.

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?

Schema description coverage is 100%, so country_code is fully documented in the input schema. The description merely echoes 'for a given country' without adding any new semantic detail, so it meets the baseline without enhancing understanding.

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 a specific verb ('List'), a precise resource ('areas (regions)'), and the exact scope ('where numbers can be purchased for a given country'). It clearly distinguishes from sibling tools like list-countries and list-numbers by specifying the purpose and required input.

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 implies usage by requiring a country_code, but does not explicitly explain when to prefer this tool over alternatives such as list-countries or list-numbers. There is no exclusion guidance or mention of scenarios where this tool is inappropriate.

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