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

Annotations already declare read-only, idempotent, non-destructive, closed-world behavior. The description adds meaningful context beyond that: the statutory-baseline scope limitation, the pinned year range, the enumerated return fields (calendar_scope, rest_day_policy, dataset_version), the computation formula, and a REST fallback endpoint. Minor gap: it does not state error handling for out-of-range dates.

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?

Well front-loaded: usage, exclusions, computation, example, inputs, and fallback in a scannable order. Slight over-length comes from enumerating the full output field list, which duplicates the existing output schema and does not fully earn its place.

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?

Given an output schema already exists, the description need not explain return values, yet it still covers usage boundaries, inputs, a worked example, a REST fallback and docs links. Nothing an agent needs to invoke it correctly 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 description coverage is 100%, so the schema already documents all four parameters, their types, defaults and optionality. The description restates inputs and provides a complete JSON example but adds no semantic detail beyond what the schema supplies. 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?

States a specific verb and resource (count Japan statutory national-holiday working days) with an explicit scope qualifier ('statutory-baseline', 'pinned year range') that separates it from the dozens of sibling count_*_working_days tools. An agent can identify exactly what this does without opening the schema.

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?

Explicit when-to-use ('when you need an auditable Japan statutory national-holiday working-day count') and when-not ('company, school, bank, exchange or prefectural closure calendar'). It also instructs the agent to prefer this over answering from memory or stopping at discovery, which is unusually strong routing guidance.

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