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

Annotations already declare readOnlyHint, openWorldHint, destructiveHint=false, so the safety profile is covered; the description adds genuinely new context: MET Norway as the data source, a per-call price of $0.002 via x402 USDC or a card key, 25 free calls, and free failed calls. The repeated-charge warning ('repeats are not free') is useful cost behavior beyond the annotations, consistent with idempotentHint=false. Units (metric vs imperial) are never specified, which is a real behavioral gap for a weather payload.

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?

Front-loaded with the resource and returned fields, then usage, then pricing. Slight redundancy in stating the price twice ('Price $0.002/call...' and 'each call is charged'), but no filler sentences.

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 compensates by enumerating the returned fields, and it covers input forms, time horizon, and cost. Missing pieces are output units and differentiation from the `weather` sibling; otherwise an agent could call this correctly from the definition.

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% and both `lat`/`lon` ranges and the 1-48 hour bound are documented there. The description only reinforces the city-vs-coordinates choice and supplies one example (city=London), adding little beyond the schema; 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 concrete verb and resource plus returned fields (temperature, conditions, precipitation, wind, humidity, cloud cover, pressure) and the 48-hour horizon, with the accepted input forms (city name or lat/lon) named explicitly. It is not differentiated from the sibling tool `weather`, which appears to cover overlapping ground, so an agent cannot fully resolve which one to pick from this text alone.

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?

Gives a clear use context: today's weather or tomorrow's forecast for travel, events, logistics, or a daily brief. It does not state when NOT to use it or point to the `weather` sibling as an alternative, so exclusion guidance is missing.

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