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

The description discloses important behavioral details: it returns synthesisPossible=false when the sun never gets high enough, and it uses clear-sky assumptions. Since no annotations are provided, the description carries the burden, and it covers the key edge case and modeling context, though it doesn't detail the underlying calculation model further.

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 three sentences, front-loaded with the core purpose, and each sentence adds distinct value (what it returns, edge case, when not to use). No filler or redundancy.

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?

Despite having no output schema, the description explicitly summarizes the return values (when UV is strong enough, best hour, clear-sky minutes, optional atTime minutes, and synthesisPossible=false). It also covers the single-day scope and sibling distinction, making it complete for selection and invocation.

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 covers 100% of parameters with descriptions, so the baseline is 3. The description adds minimal parameter context beyond restating the atTime behavior that the schema already documents, providing no additional meaning or syntax details.

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 clearly defines the tool as providing the solar vitamin D synthesis window for one specific day, listing what it returns (UV threshold, best hour, minutes needed, optional atTime calculation). It distinguishes from get_vitamin_d_year by explicitly stating the single-day scope.

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?

It explicitly states when to use the tool ('Only for single-day questions') and provides a direct alternative for other cases: 'call get_vitamin_d_year instead of calling this once per date.' This gives clear usage direction.

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