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

With no annotations at all, the description carries the full behavioral burden and does well: billed cost per call, the required Authorization: Bearer key, mandatory CC BY 4.0 attribution embedded in every response, and data latency implied by forecast source. The gap is that it never says what happens if lat/lon are omitted, even though the schema marks all three parameters optional with null defaults.

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 capability and source, then constraints, then a compact parameter list — no filler sentences. It is dense but every clause carries operational value; the parameter rundown is slightly compressed into a single trailing sentence.

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?

An output schema exists, so return-shape explanation is not needed, and cost, auth, attribution, and source are all covered. What is missing is unit convention (Celsius vs Fahrenheit, mm vs inches) and the null-coordinate fallback, both minor for a straightforward retrieval 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 description coverage is 0%, so the description must compensate and it does fully: lat valid range -90..90, lon range -180..180, hours 1-72 with a stated default of 24. This is more meaning than the bare string-typed schema conveys on its own.

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 names the exact resource and granularity: current conditions, hourly forecast, and daily min/max temperature and precipitation, plus the upstream source (MET Norway). The clause 'Coordinates only, no city geocoding' cleanly separates it from geocoding/ip_geo style siblings without opening a schema.

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?

It states a real usage constraint ('coordinates only') and a cost/auth precondition, which implicitly tells the agent it must already hold lat/lon. However, no alternative tool is named (e.g. ip_geo to derive coordinates) and there is no explicit when-not guidance beyond the geocoding exclusion.

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