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

Annotations already establish the read-only, idempotent, non-destructive safe profile. The description adds useful behavior beyond that: rates are the same regardless of caller location, prices include EUR and USD, and announced price changes are surfaced. There is no contradiction with the annotations.

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 compact and front-loaded: the first line states the core purpose and output list, while the second gives concrete query patterns. The list of returned elements is dense but each item earns its place by clarifying scope.

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?

Even without an output schema, the description enumerates the relevant return contents: every rate line, the cheapest price, announced price changes, page URL, and app download links. It also clarifies caller-location independence, which is important for international-calling queries. The only mild gap is exact response structure, which is acceptable given the tool's simplicity.

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 coverage is 100%, so the schema already fully documents the country and language parameters. The description reinforces that the query target is a country through phrases like 'calling a country' and examples like 'call X', but it adds no new format, constraints, or parameter-specific details.

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 states what the tool returns: 'Current eFon per-minute prices (EUR and USD) for calling a country' plus rate lines, cheapest price, and related links. The query intent examples make the resource unmistakable, but it doesn't explicitly differentiate itself from the sibling compare_call_rates.

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 gives concrete user intents like 'how much does it cost to call X' and 'cheapest way to call X', which clearly signal when to invoke the tool. It lacks explicit exclusions or mention of alternatives like compare_call_rates, stopping short of full alternative routing.

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