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

No annotations exist, so the description carries the full burden, yet it only discloses the date format and the 'PRO' tier marker. It says nothing about the return value (a boolean?), behavior on invalid or non-existent dates, or that access_token is needed to avoid rejection beyond what the schema hints.

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?

One sentence plus a tier marker, front-loaded with the key format constraint and free of filler. 'PRO.' is terse to the point of being cryptic but it is at least compact.

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 lookup with a self-evident boolean result and no output schema, the description is close to sufficient. The remaining gap is failure behavior for malformed dates and what the PRO label implies for auth.

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 50%: access_token is documented in the schema, and the description compensates for the bare `date` parameter by specifying the YYYY-MM-DD format. That is a genuine addition beyond the schema, though nothing is said about range limits or timezone assumptions.

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 whether') plus a precise resource ('a Japanese public holiday') and pins the input format YYYY-MM-DD, so its job is unambiguous. It doesn't explicitly contrast itself with next_holidays or year_list, which is the only thing keeping it from 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?

There is no statement of when to use this versus next_holidays (upcoming holidays) or year_list (bulk enumeration). The agent must infer the routing from the names alone.

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