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

With no annotations, the description carries the full burden and does substantial work: it discloses the data source and model, that the last day may be partial, the declared units, the exact model run, and a per-call price with payment rail (x402/USDC). What it omits is failure behavior (invalid coordinates, outages) and whether the paid call is metered or cached, which matters for an agent making cost-sensitive decisions.

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 sentences with no filler; the selection trigger comes first and the data/pricing detail follows in a dense but readable clause chain. Slightly over-packed — the model-run and units detail could be compressed — but nothing is redundant with the 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?

There is no output schema, so the description usefully enumerates the per-day return fields (min/max temperature, precipitation, strongest wind, midday symbol) plus units and model provenance. It leaves the response envelope and error cases unstated, which is a modest gap for a paid, no-output-schema 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 100%, so lat/lon/days ranges and the default are already documented. The description only adds 'any point on Earth' (global coverage) and the nine-day ceiling, both of which are already implied by the schema bounds — baseline 3 is appropriate where the schema does the heavy lifting.

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 (day-by-day weather forecast), plus scope: any point on Earth, up to nine days, sourced from the Norwegian Meteorological Institute. The 'multi-day' framing implicitly separates it from the sibling weather_now, which is the only other weather tool in the list.

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?

Opens with an explicit usage trigger ('when an agent is choosing a date and has to justify the choice'), which gives a concrete decision context rather than generic guidance. It stops short of naming the alternative (weather_now) or stating when not to use this tool, so it is clear but not complete routing guidance.

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