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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the description's job is lighter. It adds real context: the data revision date (2025-10-01), that it is an estimate rather than an official quote, and the specific return contents. It omits any rate-limit or failure-mode notes, keeping it from a 5.

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?

It is long but densely front-loaded: the core verdict and price purpose lead, the detailed rules and revision date follow, and no sentence is filler. The heavy parenthetical nesting slightly hurts scannability, so not a 5.

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?

There is no output schema, so the description carries the full burden of describing returns, and it does — verdict, Yamato size class, prices, send-by date, recommendation, official sources. For a 12-param, optional-heavy calculator, nothing an agent needs to invoke or interpret 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 baseline is 3. The description goes further by supplying domain meaning the schema lacks: the 161–250 cm reservation band with its ¥1,000 unreserved fee, the 250 cm / 30 kg prohibition, the ¥100 drop-off discount, and that Yamato bills on the larger of size or weight class.

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 names a specific resource (a bag's outside size/weight → Shinkansen oversized-baggage rule + Yamato TA-Q-BIN price) and states the exact scope it covers (which lines, which size bands). An agent can distinguish it immediately from siblings like japan_customs_allowance_check or japan_tax_free_refund_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?

It gives clear triggering context — 'call this instead of guessing' and a warning that many sites and Yamato's own English page show stale prices — which tells the agent when this tool beats its own knowledge. It does not explicitly name a sibling alternative or a when-not-to-use condition, so it stops short of a 5.

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