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

Annotations already cover the safety profile (readOnly, idempotent, not open-world), and the description adds real behavioral context beyond them: substitute holidays are included, the omitted-date default is JST-based, and the data source is the Cabinet Office. It does not describe the shape of a negative result (what is returned for a non-holiday), which is the remaining 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?

Two short sentences, front-loaded with what is checked and returned, followed by the default behavior and source attribution. Every element is relevant to an agent; the source citation is minor but supports trust in the data.

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 single-optional-parameter read tool with no output schema, the description covers purpose, default behavior, holiday scope, and data provenance. Only the negative-result behavior is left implicit, which is a small omission rather than a blocker.

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 formats (YYYY-MM-DD / YYYYMMDD) are already documented, giving a baseline of 3. The description adds the timezone qualifier ('日本時間') for the omitted-date case, which the schema does not state, so it earns slightly above baseline.

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 states a specific verb+resource: it tests whether a date is a Japanese national holiday or substitute holiday and returns the holiday name. That is clearly distinct from the sibling list_holidays, though the distinction is conveyed by implication rather than stated outright.

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 says the date may be omitted, in which case today (Japan time) is used, which gives some usage context. It never explicitly routes the agent away from this tool toward list_holidays for range or bulk queries, so the when-to-use guidance remains implied.

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