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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description usefully adds that only 'measured' cities appear in the ranking and that results are ordered worst-first by default, but says nothing about result size (limit) or what a ranking entry contains. With annotations in place, that is adequate but not rich.

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?

A single dense sentence with a colon-delimited list; the core purpose and ordering are front-loaded before the parameter details. Efficient for the amount of information carried, though the embedded examples make it slightly heavy.

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 five-parameter tool with no output schema, the description covers time modes, ordering, and country filtering, but never addresses the limit parameter or what a ranking entry looks like (city plus PM2.5 value?). An agent can call it, but not fully predict the result shape.

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 only 40% (limit, order, and window carry no schema descriptions), so the description must compensate. It partially does: it gives example formats for period (2026-09-30, 2026-W40, 2026-09, 2025) and country, and states the worst-first default, but it never mentions the limit parameter or the cleanest option. The 'year to date' phrasing also sits awkwardly against the schema's 'year' enum value.

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 names a specific resource (measured cities) and a specific metric (average PM2.5), and states the default ordering ('worst first'). This is clearly distinct from the ranking-free siblings city_air and city_history, though those siblings are never named to confirm the contrast.

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?

It sets out the two time-selection modes (rolling window vs. past period) and the optional country filter, which implies usage but never states when to prefer this tool over city_air or city_history. No exclusions or prerequisites are given.

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