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

Annotations already declare readOnly, idempotent, non-destructive and non-open-world, so the safety profile is covered; the description earns credit for adding computation semantics the annotations cannot express — the mean-of-latest-sensor-reading aggregation and the 60-minute staleness cutoff. It does not address rate limits or failure behavior when no sensor or city is in range, which the schema only partially covers via the 50 km rule.

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?

The return payload is front-loaded in the first clause and the invocation hint is a short separate sentence. The result clause is dense and run-on (nested parentheses listing seven weather fields), but essentially every clause carries information an agent needs.

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?

With no output schema, the description carries the full return-shape burden and does so thoroughly — PM2.5 plus category, current weather sub-fields, and the prior-day summary. Combined with 100%-covered parameters and full annotations, nothing material is missing for correct invocation.

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%, so the schema already documents lat/lon/city/lang/country in detail, making the baseline 3. The description adds only the either/or framing of city vs lat/lon, with no extra syntax, precedence, or default behavior beyond what the schema provides.

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 resource (PM2.5 now for a city) plus the exact composite payload: EPA category, current weather fields, and the last completed day. The 'now' framing plus the explicitly named daily historical component inherently separates it from get_air_quality_history, get_air_quality_monthly, and get_city_forecast.

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 closing 'Pass city or lat/lon' gives concrete invocation guidance on the two mutually exclusive location modes, but there is no statement about when a caller should prefer this over get_air_quality_history, get_air_quality_monthly, or get_city_forecast. Usage is implied by the word 'now' rather than stated.

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