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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description usefully adds input strictness (numeric year only, real dates in YYYY-MM-DD, no combined modes) but says nothing about return shape, ordering, or behavior when no parameters are supplied.

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?

Purpose is front-loaded in one sentence, followed by examples and then constraints; nothing is padded. Minor deductions for a missing separator/space between the example JSON and the following sentence, which slightly hurts readability.

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?

For a three-parameter read-only lookup with no output schema the core is covered, but with zero required parameters the description never states what happens on an empty call (all holidays? error?). That is a meaningful gap for a tool callable with no arguments.

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 coverage is 100%, so the baseline is 3, and the description earns above that by adding genuine constraints: year must be a numeric value rather than the string "2026", and from/to must be existing dates rejecting slash or compact formats. This clarifies edge cases the schema's type declarations do not fully convey.

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 ('指定した年または期間の日本の祝日一覧を返します') with the scope (Japanese holidays, year or date range). It does not explicitly contrast itself with siblings like is_holiday or business_days_between, so it falls short of a 5.

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 shows the two accepted call shapes and that year and from/to are mutually exclusive, which is solid invocation guidance. However it never says when to prefer this tool over is_holiday or business_days_between, so usage selection remains implied.

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