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

With no annotations, the description carries the burden. It disclosesspecific behavioral details of the return structure: monthsWithSun includes partial months via byMonth[].viableDays, solidMonths is defined, exactViableSpan gives season boundaries, and summary holds per-year aggregates. This adds meaningful context beyond 'returns data', though it does not explicitly state read-only semantics (implied by 'get').

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?

The description is three sentences, each earning its place: the opening states the tool's purpose, the middle explains the return fields, and the closing gives usage guidance. There is no filler or repetition of schema details.

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?

Given the tool's complexity (9 params, no output schema), the description covers the essential context: what the call returns, how to interpret field semantics, and when to use it vs. an alternative. It provides enough to select and invoke the tool correctly without needing to infer behavior from sibling tools.

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%, so the schema already documents all 9 parameters. The description adds no new parameter-specific semantics beyond mentioning 'for a location', which is redundant with lat/lon. The baseline of 3 applies because 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?

The description clearly states the tool returns a whole year of solar vitamin D data for a location, with a specific verb ('get') and resource ('year'). It distinguishes from the sibling tool get_vitamin_d_window by explicitly contrasting year vs. individual dates.

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?

Explicit guidance is provided: 'Use this for any question about months, seasons, winter/summer or "when during the year can I…"' and it names the alternative with direction 'never probe individual dates with get_vitamin_d_window for that.' This is a clear when-to-use and when-not-to-use statement.

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