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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered. The description adds one genuinely non-obvious behavioral rule (station vs model-estimate cities cannot be combined), but it does not say whether mixing is an error, a silent filter, or how results are grouped, so the added context is partial.

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 short sentences, front-loaded with the core action and scope, then a constraint. Nothing is padded and there is no preamble.

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 parameters, annotations covering safety, and no output schema, the description is serviceable but thin. An agent still cannot tell what a result looks like per city or how a station/model-estimate mix is handled, which are the main open questions for this tool.

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 50%: month and the cities item type are documented, but the array itself and the mixing rule are not. The description restates the 2-5 bound (already in minItems/maxItems) yet usefully flags the station/model-estimate distinction that the schema cannot express, so it adds some meaning beyond the schema.

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?

"2-5 cities side by side for one month" gives a concrete verb (compare side by side), resource (cities), and scope (single month, 2-5 entries). It is clearly distinguishable from a single-city sibling, but it never names an alternative, so differentiation is inferred rather than stated.

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?

The phrase "side by side for one month" implies the multi-city, single-month use case, and "Station and model-estimate cities are not mixed" gives one real selection constraint. However, there is no explicit when-to-use versus city_month or best_time, and no statement of what to do if the constraint is violated.

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