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

With no annotations, the description carries the full burden and does disclose the data source (live Open-Meteo forecast), the per-day result shape, and the presence of a bestDay aggregate. It does not cover failure modes (polar night, forecast outage, null bestDay) or confirm read-only/network-dependency behavior, leaving a moderate gap for a 9-param external-data tool.

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?

One front-loaded paragraph that leads with what it returns and ends with the routing rule. The three quoted example questions are slightly verbose but earn their place by disambiguating from the single-date sibling.

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 usefully enumerates the return fields and the bestDay aggregate, and the 100%-covered input schema handles parameters. It is complete enough to invoke correctly, though error/edge-case behavior for a live external forecast is unaddressed.

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 100% and the schema is unusually rich, documenting defaults and semantics for age, skinType, targetIU, days, elevationM, exposedSkinFraction, and timezone. The description adds no parameter-level detail beyond 'at a location', so the 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 specific verb+resource (multi-day vitamin D sun forecast via live Open-Meteo) and enumerates the per-day outputs: peak UV, average cloud cover, synthesis window, minutes needed, and bestDay. It explicitly distinguishes itself from the sibling get_vitamin_d_window, so an agent can route correctly without opening schemas.

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 explicit when-to-use triggers ('which day this week should I go out', 'will it be better tomorrow', 'when's my next chance') and an explicit anti-pattern: don't call get_vitamin_d_window once per date. The alternative and the condition that selects it are both named.

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