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

Annotations already declare readOnlyHint, idempotentHint, non-destructive, and closed-world, so the safety profile is covered. The description adds value by naming the returned coverage dimensions, but says nothing about pagination, filtering behavior, or result size, which is modest additional context given the low-complexity read.

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?

A single front-loaded sentence with no filler; the resource and returned fields come first. It is appropriately terse for a simple lookup tool.

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 low-complexity read-only listing with no output schema, the description conveys the core purpose and return dimensions. The gap is the unexplained 'countries' parameter, which leaves the agent guessing about filtering behavior.

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 0% and the single 'countries' parameter is undocumented in both schema and description. The description does not explain whether passing countries filters the list, is required to scope results, or what string format is expected, so the key semantic is missing.

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?

States a specific verb (List) and resource (supported countries) and enumerates the data dimensions returned (voice, SMS, registration, onboarding speed). It is clear what the tool does, though it does not explicitly differentiate itself from overlapping siblings such as get_capabilities or get_number_catalog.

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?

There is no when-to-use or when-not-to-use guidance and no mention of alternatives, despite several catalog-style siblings that could overlap. The agent must infer the selection criteria entirely on its own.

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