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

Annotations already cover read-only, idempotent, open-world behavior, so the bar is lower; the description adds real value by naming the upstream source (EPA/NWS daily forecast) and enumerating what comes back, including UV Alert status and the hours when UV is 3 or higher. It stops short of stating freshness/caching or failure behavior for invalid locations.

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 tight sentences: location scope first, returned fields second, and a closing nudge that the model's training data cannot know today's UV. No filler, and the most decision-relevant information is front-loaded.

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, describing the return payload (index, category, advice, alert, hourly peak, hours >= 3) is necessary and done well, and all parameters are covered by the schema. Only minor gaps remain, such as unit/scale conventions or behavior when a location is ambiguous or unsupported.

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 all three parameters (zip, city, state) are already documented with formats and examples. The description only restates the input pattern ("a US ZIP code or city and state") without adding new syntax or constraints, which matches the baseline for full schema coverage.

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 and resource: "Today's UV Index forecast for a US ZIP code or city and state, read now from EPA." The word "Today's" implicitly separates it from the hourly sibling, but neither sibling is named explicitly, so differentiation relies on the agent inferring it.

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 context is implied by "Today's" and by the geographic scope (US ZIP or city+state), but there is no explicit statement of when to use this versus get_uv_index_hourly or explain_uv_index, and no exclusions. The agent must infer routing from the names.

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