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

Annotations already cover the read-only, non-open-world profile, and the description adds genuine behavioral context beyond them: model estimates are labelled as such, fire/smoke/volcano attributions are 'named as likely causes, never confirmed', and the tool explicitly excludes forecasts. These are useful epistemic caveats an agent needs to frame results.

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?

A single dense sentence, but it is front-loaded with the core value ('PM2.5 now in a city') and every clause adds a distinct output element or caveat. No padding or repetition, though the run-on structure is heavier than necessary.

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 carries the full burden of describing returns, and it does so thoroughly — hourly value, four averaging windows, rank context, EPA and WHO comparison, and attribution notes. Nothing an agent needs to call or interpret this tool 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?

There is a single required parameter with 100% schema description coverage, and the schema already explains the accepted formats (page path, SmogRank URL, or name) plus the find_city fallback. The description adds nothing about the city argument, 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-and-resource pair (latest hourly PM2.5 for a city) and enumerates exactly what the payload contains, so an agent knows the tool's output shape from the description alone. It distinguishes itself from city_history implicitly via 'now' and 'No forecasts', but never names the siblings outright.

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 rather than stated: 'No forecasts' and the note that monitorless cities get a labelled model estimate sketch the boundary, but there is no explicit when-to-use-this-vs-city_history or vs rank/rankings guidance. The pointer to find_city for path resolution lives in the schema, not the description.

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