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

Annotations already declare readOnly/idempotent/non-destructive/openWorld=false, so the safety profile is covered. The description adds substantive behavioral detail beyond that: shared-code handling, and that the result includes capital, example number, an eFon rate page, cheapest per-minute callback rate, and a one-ring scam warning. No auth/rate-limit caveats, but this is well above the annotation baseline.

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?

Front-loaded with the core purpose, and every clause (shared codes, example queries, return contents) earns its place. It is a single long run-on sentence with a slightly promotional tail ('Includes the cheapest eFon per-minute rate...'), which keeps it from a 5.

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: it names the country/countries, capital, example number, rate page and scam warning an agent will get back. Nothing an agent needs to call this correctly is missing.

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 both parameters (code, language enum with default) are already documented, including the accepted formats. The description's mention of shared codes adds a little interpretation value but no syntax beyond the schema, so the baseline 3 applies.

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+resource ('calling-code lookup: which country ... a code belongs to') and clarifies the shared-code edge case (+1, +7, +44). It is clearly distinguishable from siblings get_call_rates, compare_call_rates and how_to_call, which deal with rates and dialing procedure rather than country identification.

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?

Gives concrete trigger phrases ('which country is +36', 'who is calling me from +233', 'what does 00252 mean', missed call from an unknown foreign number), which is clear usage context. It does not, however, explicitly state when to prefer a sibling (e.g. how_to_call) or any exclusions, so it stops short of a 5.

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