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

Annotations already establish read-only, idempotent, non-destructive behavior; the description adds genuine behavioral context: the AirNow source, the CONUS geographic limitation, the AQI band scale, and that forecast is opt-in. No statement in the description contradicts the annotations.

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?

Each of the four sentences earns its place: resource and return scope, AQI scale, default-versus-expanded usage guidance, and a concrete example. The identifying scope is front-loaded, and there is no filler or repetition of schema descriptions.

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 an output schema present, return-format details need not be repeated. The description covers data source, geography, default behavior, optional expansions, and an example, while the schema covers coordinate/location validation and constraints. An agent has what it needs to invoke the tool correctly.

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?

The input schema describes all five parameters at 100% coverage, so the baseline is 3. The description adds strategy on top of the schema by labeling the default call as 'cheap' and showing a complete example combining location, pm25, and include_forecast, which helps an agent compose parameter combinations rather than merely filling names.

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 opens with a concrete resource and scope: 'AirNow air quality at a location (CONUS)' and lists exactly what is returned: current overall AQI, per-pollutant detail, and forecast. It is clearly distinct from sibling weather tools because it identifies the AirNow source and AQI domain rather than generic current conditions or observations.

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 gives clear context for when to use the tool (for AirNow AQI at a location) and provides parameter-selection guidance: the default ['aqi'] is the 'cheap headline call', and additional pollutants or include_forecast should be added 'when the user digs in'. It does not explicitly name alternative sibling tools or state exclusion criteria, which keeps it from a 5.

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