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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so the safety profile is covered. The description adds genuinely behavioral content beyond that — that the result is split into a free tier (SIP/VoIP/app) versus a paid per-minute range to real phone numbers — which tells the agent how to interpret the response, though it says nothing about price freshness, coverage gaps, or rate limits.

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?

One sentence, front-loaded with the action and the result shape, with the disambiguation parenthetical placed at the end. No filler, no restatement of the title.

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?

With an output schema present, the description is not obliged to explain return values, and the single required parameter is fully specified in the schema. It is complete enough to call correctly; only minor gaps remain, such as whether prices are cached or how often they refresh.

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?

There is a single parameter and schema description coverage is 100%, so the schema already documents the ISO 3166-1 alpha-2 format and example. The description only reinforces the semantics of 'country' as the forwarding destination, which is the baseline 3 when the schema does the heavy lifting.

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 and resource ('get what forwarding calls to a country costs') and immediately enumerates the two price components returned: free destinations (SIP, VoIP, app) and a per-minute range for the country's phone numbers. The final parenthetical explicitly distinguishes it from the sibling get_calling_rate, so an agent can route between them without opening either schema.

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?

Names the alternative tool and the exact condition that selects it: 'use get_calling_rate for one exact number.' That is an explicit when-to-use-this-vs-that rule, the pattern that earns top marks for routing guidance, and it is placed inline where the ambiguity would otherwise arise.

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