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

With no annotations, the description carries the disclosure burden and does well on the important point: it names the live Open-Meteo UV/cloud data source and the clear-sky model fallback when unreachable, which is real behavioral context an agent cannot get from the schema. It omits latency, failure/caching behavior, and any note that this is a non-mutating computation, which keeps it short of a 5.

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?

A single front-loaded sentence that answers what the tool does, what data backs it, what it falls back to, and what it returns, with no filler. The parenthetical fallback note is terse and load-bearing.

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?

For an 8-parameter computational tool with full schema coverage and no output schema, the description supplies the return-value summary (UV index, minutes needed, window times) and data-source caveat, which is enough to call it correctly. A slightly fuller statement of what an 'unreachable' response looks like would close the remaining gap.

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 all 8 parameters are richly documented with ranges and defaults, so the schema already does the parameter work. The description adds nothing parameter-specific beyond 'at a location', meeting the baseline 3 for high-coverage schemas.

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+scope: whether RIGHT NOW is a good moment for vitamin D synthesis, plus what it returns (current UV index, minutes needed, window open/close). The temporal 'RIGHT NOW' framing implicitly separates it from forecast/window siblings like get_sun_forecast and get_vitamin_d_window, but no sibling is named, so an agent must infer the boundary.

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?

Usage is implied by the 'right now' phrasing (use this for present conditions, other tools for future windows or yearly comparisons), but the description never states when to pick this over estimate_sun_session or get_vitamin_d_window. No explicit alternatives or exclusions are given.

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