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

With no annotations, the description carries the full behavioral burden. It does disclose a required authorization scope, which is genuinely valuable, and 'list' plus 'sold' implies a safe read, but it says nothing about pagination, result size, or ordering.

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 compact sentence with the subject front-loaded and no filler. Every clause (virtual numbers, rental duration, dial codes, scope) adds information.

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 no-parameter, no-output-schema read tool this covers the essentials: what is returned and the permission needed. The one gap is that it never clarifies how it differs from the neighboring list_countries tool.

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 tool takes zero parameters, so there is no parameter semantics to convey; the baseline of 4 applies. The description's mention of dial codes is return-value context rather than parameter guidance.

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 resource (countries where virtual numbers are sold) and adds useful scope detail ('with dial codes'), making the returned data predictable. It does not, however, contrast itself with the sibling list_countries, so an agent must infer the distinction from the 'virtual numbers' qualifier alone.

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 supplies one prerequisite ('Requires the numbers scope'), which is actionable context, but gives no when-to-use guidance or explicit routing versus list_countries or list_esim_destinations. Usage is only implied by the resource name.

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