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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=true, and destructiveHint=false. The description adds meaningful behavior beyond that: the data is read now from EPA, times are in the place's local time, and the response includes each hour's EPA band, the peak hour, and the window when UV is 3 or higher. It does not cover error cases or non-US coverage limits.

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?

Two sentences, front-loaded with the resource and scope before the usage examples. Every phrase earns its place, with no redundant or filler wording.

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?

There is no output schema, but the description explains the key return elements: hourly UV values with EPA bands, the peak hour, and the UV>=3 window. Inputs are fully documented by the schema and description, so an agent has enough detail to call and interpret this simple read-only forecast tool.

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 already documents ZIP versus city plus state with examples and length limits. The description restates the input modes and adds only that results are in the local time of that place; it does not add syntax, validation, or edge-case meaning beyond the schema. Baseline 3 applies when 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?

States a specific verb and resource: an hour-by-hour UV Index forecast for a US ZIP code or city/state, in local time, sourced from EPA. It is distinguishable from get_uv_index_today by the 'hour by hour' scope and from explain_uv_index by being a forecast rather than an explanation, but it never explicitly names or routes against either sibling.

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 concrete usage contexts: 'when is the sun strongest today' and 'what time is safe to be outside' questions. It does not state when not to use it or explicitly direct the agent to get_uv_index_today or explain_uv_index for other needs, so it is clear context without exclusions rather than full routing guidance.

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