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

With no annotations, the description carries the full burden, and it discloses the most consequential behavior an agent must know: this is a paid call at 0.001 USDC via x402, with the two-step 402-then-pay flow documented in the schema. It adds that results are 'current' rather than forecast, but says nothing about failure modes, rate limits, or what happens when no location argument is supplied.

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, zero filler: the returned metrics first, the cost second. Nothing is repeated from the schema and nothing could be cut without losing information.

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?

There is no output schema, and the description compensates by enumerating the metrics returned, plus the per-call price. The remaining gap is that all four parameters are optional, so the description should state what happens if neither a place nor coordinates is given.

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%, so lat/lon/place/paymentProof are all documented structurally and the payment flow is spelled out in paymentProof's own description. The description adds only the mapping of 'place name or coordinates' onto those fields, so the baseline 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?

Names a specific resource (current US AQI, European AQI, PM2.5, PM10, ozone, NO2, UV index) and the two accepted locators (place name or coordinates), so an agent knows exactly what comes back. It doesn't explicitly contrast with the sibling 'weather' tool, which is the nearest potential source of confusion, so it stops short of a 5.

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?

'By place name or coordinates' implies the selection between geocoded and raw-coordinate lookups, but there is no explicit when-to-use/when-not guidance and no mention of the 'weather' sibling as an alternative for forecast data. Usage is inferable but not spelled out.

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