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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered. The description adds context that coverage is uneven worldwide, that the catalog is bounded (~153 countries), and that the date span reveals recency of data. This goes beyond what annotations state and helps the agent understand the tool's limitations without contradicting any annotation.

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 compact sentences front-load the core value (country-level coverage) and then the practical use (availability check before find_locations). No filler or redundancy; every sentence earns its place.

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?

Given the tool is read-only, idempotent, has a fully documented 2-parameter schema, and includes an output schema, the description fully covers what the agent needs to decide when and how to call it. It explains the data's meaning, the usage path, and the coverage caveat. Nothing critical 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 both parameters are described in detail: query explains case-insensitive exact-vs-substring behavior and the two-letter ISO code rule; parametersId explains filtering by id, gives an example, notes multiple ids per pollutant, and mentions composition with query. The description itself does not add parameter-level semantics beyond what the schema provides, so the baseline of 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?

The description uses a specific verb ('list') with a clear resource ('countries') and states exactly what the catalog contains: id, ISO code, name, date span, and measured parameters. It also frames the purpose as an availability check and a pre-step to openaq_find_locations, making it distinct from siblings like openaq_list_parameters or openaq_find_locations.

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 description explicitly tells when to use it: before a regional sweep and before calling openaq_find_locations, and gives concrete questions it answers (e.g., 'which countries have NO2 monitoring?', 'whether a country has recent data'). It does not explicitly state when not to use it, but the context is clear and no direct sibling competes for this narrow role, so exclusion is not critical.

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