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

With no annotations, the description carries the full burden and does disclose the return contents: months with sun, exact season span, viable days per year, and a rankedByViableDays ordering, for war-free planning. It does not state that this is a pure read/compute with no side effects or persistence, which is the one meaningful gap.

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, front-loaded with the core capability, then the return shape, then the sibling routing. The quoted example question ('Madrid vs Berlin vs Oslo...') is illustrative but slightly decorative rather than informative.

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?

No output schema exists, yet the description sketches the response shape (per-place months, season span, viable days, ranking), which is the critical missing structured info. Combined with full param coverage this is nearly complete; only side-effect/read-only semantics are unstated.

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 age, skinType, targetIU, exposedSkinFraction and place fields are already fully documented in the schema. The description only restates the 2-to-5 places constraint, adding no syntax or defaults beyond structured data. Baseline 3.

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 (compare) and resource (vitamin D year) with an explicit cardinality bound (2 to 5 places) and an output-oriented framing ('side by side in ONE call'). It is clearly distinguishable from the sibling get_vitamin_d_year, which it names.

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?

Explicitly states when to prefer this tool: 'Use this instead of calling get_vitamin_d_year once per city'. It also gives the exclusivity reason ('only this tool can draw the years on a shared axis'), which tells the agent when the sibling is insufficient.

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