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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds genuinely new behavioral context — that per-engine country support differs and some engines block certain countries — which an agent would not infer from annotations or schema. No mention of result shape, but an output schema exists, so that burden is not on the description.

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, zero filler, with the scope (geo-targeting country codes) front-loaded before the optional-parameter guidance. Every clause carries 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?

Single optional enum parameter, full schema coverage, output schema present, and all four annotation hints supplied. The description adds the one non-obvious semantic (per-engine variation), so nothing an agent needs to invoke 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% and the enum is self-documenting, so the baseline is 3. The description adds value beyond the schema by explaining why the parameter matters — the returned set can differ per engine — rather than just restating "optionally filter by engine".

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 and resource ("List the ISO 3166-1 alpha-2 country codes") plus the scoping purpose ("supported for geo-targeting"), which distinguishes it from the sibling scrape_* tools and from list_states. An agent knows exactly what it gets back without opening the schema.

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?

"Pass a model to get the codes available for that specific engine" gives explicit conditional guidance on the optional parameter, including the motivation (engines block certain countries). It does not name a sibling alternative or state when not to use it, so it falls short of a full 5.

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