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 a critical non-obvious trait: it is paid per call via x402 (USDC on Base), and omitting payment_signature returns payment requirements. That auth/payment behavior is exactly what an agent needs. It omits error behavior, rate limits, or response-shape caveats, keeping it short of 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?

The purpose, scope, usage condition, and payment note are front-loaded in a dense but readable paragraph. It is longer than strictly necessary, with some near-redundancy between 'UK Global Tariff' and 'UK Trade Tariff', but every sentence contributes meaningful information.

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 must convey returns, and it does name the fields an agent gets back (duty rates, units, measure types, candidate codes). For a lookup tool at this complexity it is largely self-sufficient, though it does not describe the response structure or failure cases.

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 each parameter (code, query, origin, markets, payment_signature). The description adds only a little beyond it, e.g. that keyword search returns candidate codes and origin is used for UK preferential rates. Baseline 3 is appropriate.

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 states a specific verb+resource ('Customs tariff lookup by HS/commodity code or keyword') and enumerates the exact data returned: UK Global Tariff third-country duty, preferential rates by origin, VAT and measure types, and US HTS general/special/column-2 rates. An agent knows precisely what this tool retrieves and from which sources (UK Trade Tariff, USITC HTS).

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 — 'Use when an agent must classify goods (HS/commodity code) or find the import duty for shipping goods into the UK or the US' — and clarifies the code-vs-keyword distinction ('Keyword search returns candidate codes'). There are no sibling tools, so no alternatives or exclusions are needed, but none are stated either.

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