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

Annotations already declare the operation read-only, idempotent, open-world, and non-destructive. The description adds useful behavioral context beyond that: data source (currentuvindex.com), license (CC BY 4.0), and that no auth is required, plus what the response contains. No contradiction with annotations.

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?

Three sentences with each carrying distinct information: the core deliverable, the risk-category detail, and provenance/licensing/auth. The description is front-loaded with the main function and contains no filler or redundant content.

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?

This is a simple two-parameter, read-only tool with an output schema, so return-value details are already covered. The description supplies everything else an agent needs: response scope (current, ~120h forecast, 24h history), risk categories, peak forecast, data source, license, and auth requirement. Nothing critical is missing.

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?

Both latitude and longitude are fully documented in the schema with ranges, examples, and units (100% schema coverage). The description only restates 'any latitude/longitude worldwide' and adds no new parameter-level semantics, so the baseline score of 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?

The description uses a specific verb ('Get') and resource ('current UV Index, an hourly forecast..., and up to 24 hours of recent history') for any latitude/longitude worldwide, and clearly states the WHO/EPA risk categories and peak forecast are included. It is clear and the UV focus inherently sets it apart from general weather tools, but it does not explicitly name a sibling or contrast with alternatives, so it stops short of the top score.

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?

No explicit when-to-use or when-not-to-use guidance is given, and no alternative tools are named. The use case—needing UV index, forecast, or history for a coordinate—is implied by the resource description, but an agent receives no help choosing between this and general weather condition tools like weather.conditions.forecast or weather.weatherapi.current.

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