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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description usefully enumerates what is returned (native name, capital, continent, calling codes, currencies, languages, emoji flag) in the absence of an output schema, but it also advertises filter capabilities that the schema does not support, which undercuts trust.

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?

Three sentences with the first duplicating the title and the third a long comma-separated field list. The 'Country by code' sentence is front-loaded and useful, but the opening is wasted space and the field enumeration is dense and unstructured.

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 tool with no output schema, describing the returned fields is the right instinct and largely done. The gap is that the advertised filter surface does not match the two-parameter schema, leaving the agent with an inaccurate picture of how to actually constrain results.

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% for both parameters (code, lang), so the baseline would be 3. However, the description promises filtering by continent, currency, language and search, none of which exist as parameters in the schema, giving the agent a misleading impression of the callable interface that could lead to failed invocations.

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 (country data) and the lookup key ('Country by code'), and enumerates the fields returned, so an agent can tell it is a country lookup rather than, say, a city or geocoding tool. It loses a point for opening with a verbatim restatement of the title, which adds no distinguishing information.

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?

There is no statement of when to use this tool versus alternatives such as city_search, reverse_geocode or airport_info, and no exclusions or prerequisites. 'Filter by continent, currency, language or search' hints at modes but gives no selection logic between them.

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