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

With no annotations, the description carries the full burden and does disclose meaningful traits: results are staged by payment timing, sums are partial, and missing fees come back as null rather than fabricated. It does not say whether the call is read-only/pure computation, whether it hits the network, or how results are shaped for a multi-proxy comparison.

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?

Three short front-loaded sentences with zero filler; the output caveat and null behavior are stated immediately after the purpose.

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 no-output-schema estimator with 16 parameters, the description covers the key conceptual contract (per-item, staged, partial, nulls). The large gap is parameter guidance for the 11 undocumented fields, which the description leaves entirely to a thin schema.

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 only 38% across 16 parameters, so the description must compensate and it does not — no required field (price_jpy, category, country) is mentioned, nor quantity, weight, lithium, or alcohol handling. The phrase 'for one item' only vaguely gestures at per-unit pricing semantics.

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 (estimate), resource (yen costs), and scope (one item via Japan proxies), plus the pay-now / before-ship / on-arrival breakdown. An agent can tell this is a cost projection, not a shippability or proxy-comparison tool, though the overlap with compare_proxies is not addressed.

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 clause 'Partial sums only; not a landed total' usefully bounds what the result can be used for, which implies when it fits. But there is no explicit when-to-use versus siblings such as compare_proxies, and no stated prerequisites (e.g., that weight or dimensions drive accuracy).

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