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

Annotations already cover the read-only and open-world profile, yet the description adds material behavior an agent cannot get elsewhere: per-call pricing of $0.002 USDC via x402 on Base/Solana/Arc and the fact that failed calls are not charged, plus the ~6-month publication lag. It stops short of stating rate limits or pagination behavior, keeping it at 4.

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?

Front-loaded with the resource and granularity, and every sentence (data scope, geography, lag, pricing) earns its place. The opening sentence is a long run-on packing three ideas together, which slightly hurts scannability.

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?

Output schema exists, so return-shape detail is unnecessary; coverage of mode selection, geographic keys, pollutant options, data lag, and payment model is sufficient for an agent to call this correctly on the first attempt.

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?

With 100% schema coverage the baseline is 3, and the description earns extra credit by explaining the mode switch — that supplying a year yields annual summaries instead of daily values — which the schema only states per-field without the either/or framing. It also restates county-by-name-or-FIPS and the pollutant list, which is useful orientation but duplicative.

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 verb+resource (US EPA AQS certified monitor data) plus the exact granularity (daily per-monitor values vs annual summaries) and the pollutant set. An agent can immediately tell this retrieves official air-quality measurements for a county, unlike any of the unrelated directory/registry siblings.

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?

Implies the selection rule between the two modes: passing 'year' yields annual summaries, otherwise daily values (and it states the official, quality-assured, ~6-month-lag caveat, which determines when the tool is even usable). It does not explicitly say when NOT to use it or name an alternative, but the sibling set offers no competing air-quality tool, so the practical guidance is strong.

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