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

Annotations already cover read-only/idempotent safety, and the description adds substantial semantics beyond them: the own_record vs copied_record distinction, that a copied_record describes the source city rather than the named city, and that values are historical annual data rather than current AQI. This is exactly the non-obvious behavior an agent needs.

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?

Three sentences, front-loaded with what is returned, then the record-type caveat and the historical-vs-current distinction. Dense but every sentence earns its place.

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 no output schema, the description enumerates the return fields (score, grade, PM2.5 mean, unhealthy-day share, trend, yearly PM2.5) and explains the two record types. Nothing needed to interpret the result is missing.

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 city and state are fully documented in the schema. The description adds no syntax or format detail for the parameters, 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?

States a specific verb+resource ('Historical Clean Air Score... for one US city') and enumerates the returned fields. The single-city scope implicitly distinguishes it from compare_cities and rank_cities, which operate across cities.

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?

Usage is implied by the single-city framing and the note that values are historical, not current AQI, which steers an agent away from one wrong use. But there is no explicit when-to-use or when-to-prefer-compare/rank guidance.

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