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

Annotations already establish read-only, idempotent, non-destructive, closed-world behavior, so the bar is low; the description still adds real value by disclosing the cost profile ("Free") and the semantic tiering of results (ranked decisions vs facts only). It does not add auth, rate-limit, or pagination context, but none is suggested by the annotations.

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 short sentences plus a one-word cost note, all front-loaded: coverage scope first, capability tiers second, activities third, and the negative boundary ("Anywhere not listed is not covered") immediately after. Nothing is redundant with the title or schema.

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 read-only, no-required-parameter metadata tool with full schema coverage and an output schema, the description supplies everything an agent needs: what is covered, how results are graded, the closed-world boundary, and that it is free. Return-value details are rightly delegated to the output schema.

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 optional region parameter with 100% schema description coverage, so the schema already documents its meaning ("Limit to one region id."). The description does not mention the region filter or what an unfiltered call returns, which is the baseline-3 case where structured fields carry the parameter semantics.

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?

The description states a specific resource (KaiCast coverage: regions, spots, supported activities) and what each entry conveys (ranked-decision capability vs facts-only). It is clearly distinguishable from the action-oriented siblings (best_day, get_conditions, recommend_spot), though it never names them explicitly to sharpen the contrast.

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?

"Anywhere not listed is not covered" and "Free" give the agent a clear decision rule for interpreting results and a cost signal for when to call it. What is missing is an explicit statement that this should be consulted before recommend_spot/best_day for an unlisted region.

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