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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so safety is covered. The description adds real behavioral value by disclosing that the response explains the reason for closure (weekend, named holiday, bank closure, custom closed day), which goes beyond what the annotations state. It stops short of describing the exact response shape or precedence when a date qualifies under multiple reasons.

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?

A single front-loaded sentence that states the action and the returned reasons, with zero filler. The bilingual duplication doubles the surface length, but that appears to be an environment convention rather than 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 read-only, idempotent boolean-style check with a fully documented 4-parameter schema and no output schema, the agent has enough to call it correctly and knows what a negative result conveys. Only the concrete return structure (flag plus reason field names) is left unspecified.

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%, with the calendar enum and both extra_holidays/extra_business_days arrays fully documented inline, so the description carries no additional parameter burden. It doesn't add syntax or precedence detail (e.g., what happens if a date appears in both extra lists), leaving this at the baseline for a fully documented schema.

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 (check) and resource (a date's business-day status) scoped to Japan, and even enumerates the possible negative results (weekend, holiday name, bank closure, custom closed day). This clearly separates it from siblings like count_business_days, add_business_days, and last_business_day_of_month, which perform arithmetic rather than a boolean check.

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 rather than stated: an agent can infer this is the tool for 'is date X a business day?' but the description never says when to prefer it over adjust_to_business_day or how it relates to list_holidays. No explicit when-to-use, when-not, or alternative routing is provided.

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