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

Annotations already establish read-only/idempotent/non-destructive, so the safety profile is covered; the description usefully adds that rates are caller-location-independent, that data is 'live', and it enumerates the returned content (rate lines, cheapest price, announced price change, page URL, app links). That return-shape disclosure is valuable given there is no output schema, though 'live' is not defined (refresh cadence / caching is unstated).

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 resource and granularity come first, followed by the return inventory, with usage triggers last — a sensible front-loaded order with no filler. The opening sentence is heavily comma-loaded, but every clause conveys distinct 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?

With no output schema, the description carries the return-value burden and does so by listing what comes back; annotations cover the safety profile and the schema covers both parameters fully. Only minor gaps remain: error behavior for an unresolvable country and what 'live' means in practice.

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 both 'country' (multilingual names, ISO code, dialing code) and 'language' (enum, default en) are already fully documented with examples. The description adds no parameter-level detail beyond noting that rates do not vary by caller, which justifies the absence of a caller parameter but does not extend the schema semantics.

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 the resource precisely: per-minute eFon prices in EUR and USD for calling a named country, including the granularity of rate lines (mobile/landline/network). The scope ('a country', single-country lookup) implicitly separates it from compare_call_rates, but no sibling is named explicitly, so the agent must infer the boundary between this and the comparison tool.

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?

It supplies concrete trigger queries ('how much does it cost to call X', 'cheapest way to call X', 'is calling X from abroad expensive'), which maps user intent to the tool well. However, it never states when NOT to use it or names compare_call_rates/how_to_call as the alternatives for multi-country or dialing-instruction queries, so routing between siblings is left to inference.

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