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

Annotations already declare readOnly/idempotent/closed-world, so the bar is lower, yet the description adds real behavioral detail absent from structured fields: reason is Japanese text, reason_code values, null on business days, and the meaning of the estimated/unverified flags. Only the estimate-year threshold behavior is left slightly implicit.

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?

Front-loaded with the core purpose and reason codes; the bilingual duplication roughly doubles the length without adding new information, but the content itself is dense and free of filler.

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?

With no output schema, the description correctly compensates by documenting the returned fields (reason, reason_code values, flags). For a read-only single-date predicate this is close to complete; only explicit sibling routing and the estimate-year boundary are 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 description coverage is 100%, so the schema already documents date, calendar, extra_holidays, and extra_business_days, including the enum semantics of standard vs bank. The description restates the bank-closure and custom-holiday concepts but adds no format or precedence information beyond the schema, so the baseline 3 applies.

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?

Starts with a specific verb+resource: 'Check whether a date is a business day in Japan, and if not, why.' It even enumerates the possible reasons (weekend, holiday name, bank closure, custom closed day), which cleanly separates it from siblings like adjust_to_business_day and count_business_days.

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 usage is implied by the description (a predicate-style lookup for a single date), but there is no explicit when-to-use/when-not or pointer to the sibling tools that modify or enumerate business days. An agent must infer the boundary itself.

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