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

Annotations already cover readOnlyHint and openWorldHint, so the bar is lower, and the description adds real value beyond them: a per-call price of $0.003 USDC via x402, plus the upstream data source (OpenAQ). It still omits freshness/latency of station data and any rate limits, so it is not a 5.

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, front-loaded with the capability and follow-up with the cost. Every clause (pollutants, AOI category, source, price) earns its place; no filler.

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 read-only lookup with no output schema, the description adequately signals the response shape (pollutants plus AQI category). It is incomplete on inputs, though: with 0 required parameters and no schema documentation, an agent cannot tell what constitutes a valid call or how the optional location parameters interact.

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 0% across four parameters, so the description carries the full burden. "Near any place" vaguely hints at lat/lon/near, but nothing explains precedence between near and lat/lon, the units or default of radius_m, or what happens when no parameters are supplied (all four are optional).

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?

Concrete verb+resource: retrieves air quality near a place from OpenAQ monitoring stations, and it names the returned payload (PM2.5, PM10, ozone, NO2, US AQI, health category). It does not, however, distinguish itself from the siblings airquality_compare, airquality_history, and airquality_stations, so an agent cannot route between them from this text alone.

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?

There is no when-to-use statement, no when-not-to-use, and no named alternative despite three closely related air-quality siblings. Only an implicit signal ("near any place") hints at the calling context.

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