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

With no annotations, the description must carry the behavioral load. It does disclose three useful traits: a fixed 7-day window, a hard 5-station ceiling, and that the endpoint is 'PRO' (i.e. gated behind a subscription token, consistent with the access_token parameter). It does not disclose the return shape, ordering, pagination, or what happens if more than 5 ids are supplied.

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 with the capability front-loaded and the prerequisite attached to the parameter it concerns. The leading 'PRO.' is a compact tier signal, though slightly cryptic on its own.

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?

For a two-parameter read tool with no output schema and no annotations, the description covers the window, the cap, and the id source, which is most of what an agent needs. It still leaves the shape of the comparison result and the failure mode for over-limit or premium-denied requests unstated.

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%: access_token already has a description, but station_ids is bare in the schema. The description compensates by telling the agent where the ids come from (nearest_station) and how many are permitted (up to 5), which is the actionable semantics for the undocumented required parameter.

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 concrete verb-and-resource: returns the last 7 days of observations across a set of climate stations, with the cardinality cap of 5. It does not explain what the 'compare' aspect produces (side-by-side series vs. per-station blocks), and its differentiation from sibling daily_history is left implicit, but the scope is clear enough to select it.

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 parenthetical 'pass station ids from nearest_station' establishes a prerequisite workflow and the 'up to 5' cap sets a usage bound. However, it never says when to pick this over daily_history, which is the sibling most likely to be confused with it (same observations, different aggregation/window).

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