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

With no annotations, the description carries the full burden and provides valuable behavioral details: it mentions the default start time ('defaults to the day's best hour'), the physiological cap on IU, and the specific outputs (IU, average UV, clear-sky minutes-to-sunburn). It does not claim to be read-only or destructive, but the description does not require additional disclosure beyond its actual function.

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 two sentences, front-loaded with the primary use case and example questions, then a concise summary of inputs and outputs. Every sentence earns its place without redundancy or unnecessary detail.

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 (10 parameters, multiple outputs), the description adequately connects inputs to outputs and explains the tool's role in the broader domain. It does not enumerate every parameter but the schema covers those details. The absence of an output schema is partially mitigated by listing the return values (IU, average UV, minutes-to-sunburn).

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?

The input schema already provides 100% coverage with detailed descriptions for all 10 parameters, including defaults and meanings. The tool description adds context about the start time default and the output units, but does not significantly expand parameter semantics beyond what the schema offers. This matches the baseline for high 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?

The description starts with a specific verb 'Estimate' and clearly identifies the resource as a 'sun session's outcome'. It distinguishes itself from siblings by focusing on per-session estimation of vitamin D production and sunburn time, with illustrative user questions. This makes the tool's purpose unmistakable.

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?

The description explicitly states when to use the tool: 'Use for any how much did I get / can I get in X minutes or how long without burning question'. While it does not explicitly mention alternative tools, the clear usage context effectively differentiates it from siblings like get_vitamin_d_window or get_sun_forecast.

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