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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=true and idempotentHint=false, but the description adds genuinely new operational context: per-call pricing via x402 USDC or card key, 25 free calls, failed calls free, and the practical consequence that repeated identical calls are still charged. The only redundancy is "reads or computes only and changes nothing", which restates readOnlyHint.

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 output payload is front-loaded in the first sentence, then usage, example, and cost. Every sentence carries information, though the pricing clause is dense and could be split for readability, and "reads or computes only and changes nothing" is the one phrase that could be cut without loss.

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 only two fully documented required parameters and no output schema, the description compensates well by listing the exact quantities returned and the model source. It does not state units or the response shape, but for a two-parameter lookup tool this is close to sufficient.

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% and both parameters carry their own range documentation (-90 to 90, -180 to 180), so the schema does the heavy lifting. The description adds only a worked example (lat=59.33, lon=18.07), which is mildly useful but adds no coordinate-format or rounding semantics beyond the schema. 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?

"Current air quality at a point" gives a specific verb and resource, and the description enumerates the exact metrics returned (European and US AQI, PM2.5, PM10, O3, NO2, SO2, CO) plus the upstream source (Open-Meteo, CAMS). No sibling tool in the list covers air quality, so it is trivially distinguishable from elevation, uv, and ip_geolocate.

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?

"Use for health, outdoor-activity and travel decisions" gives a concrete usage context, and the example coordinates show the calling convention. It stops short of explicit when-not guidance or naming an alternative (e.g. the uv tool for UV-only needs), so it is clear but not routing-complete.

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