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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety and determinism profile is fully covered. The description adds domain content about what is returned but no operational behavior such as caching, freshness, or fallback behavior when a region code is unknown. Useful, but nothing beyond what the annotations and output schema already convey.

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?

Two sentences, the content-bearing enumeration first and the usage directive second, with no filler. The first sentence is dense with parenthetical lists but every clause maps to a real output field, so little is wasted.

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?

An output schema exists, so the description need not explain return structure, and it correctly focuses on scope and content instead. For a two-parameter, read-only lookup this is close to complete; the only gap is the missing sibling disambiguation against check_license_plate and list_license_plate_countries.

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%, and both parameters (ISO alpha-2 country, locale enum) are already described thoroughly in the schema, including the instruction to set locale on every call. The description adds no parameter-level detail (e.g. country-code case sensitivity), so the schema does all the work; baseline 3.

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 concretely enumerates the resource contents: a country's plate format (standard, size, format), plate types (diplomatic, police, taxi), and region codes grouped by region, with concrete examples (77, 199). This tells the agent exactly what data comes back. It never differentiates itself from the closely named siblings check_license_plate or list_license_plate_countries, so it stops just short of a 5.

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 second sentence gives explicit trigger conditions — 'Use it for what a plate region code means ... and a country's plate format.' That is clear, actionable context. However, it offers no exclusions and does not name the alternative tools (e.g. check_license_plate for validating an actual plate), which the routing agent would benefit from.

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