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

Annotations already cover readOnly/idempotent/closed-world, and the description adds genuine context beyond them: results are sorted by date, substitute holidays are included, and the data source is the Cabinet Office. It does not elaborate on return shape beyond ordering, but for a read-only reference tool this is solid.

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 compact sentences, front-loaded with the scope and result ordering, with the source citation appended where it belongs. No padding.

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 two-parameter read-only lookup this covers scope, substitution rules, ordering, and provenance. There is no output schema, so a brief hint of the returned record shape could add value, but nothing essential is missing.

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 both year and month are fully documented in the schema, including the omitted-month default behavior. The description only restates the year/month scoping, adding no syntax or semantics beyond the schema, matching the baseline for full 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 gives a specific verb (返します/list) and resource (日本の国民の祝日・休日, including 振替休日) with the return ordering stated. It does not explicitly distinguish itself from the sibling check_holiday, which is the closest overlap.

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?

Usage is implied by the year/month scoping ('指定した年（と月）の'), but there is no explicit guidance on when to use this versus check_holiday (single-date lookup) or any exclusions.

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