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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint false. The description adds useful context beyond annotations by disclosing the authoritative HMRC source and the breadth of returned measures, though it does not discuss rate limits or pagination behavior.

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 definition is front-loaded with what the tool returns and includes a concrete example. It is somewhat long and contains mild promotional emphasis such as 'AUTHORITATIVE', but every core sentence carries useful 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?

For a read-only tariff lookup with 100% schema coverage and no output schema, the description is complete: it explains the source, the categories of measures returned, and suitable use cases. An agent has enough information to invoke it correctly.

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 input schema already documents code, origin, and max_measures. The description mentions the 10-digit code but does not add meaning for origin or max_measures beyond what the schema provides, matching the baseline of 3 when the schema does the heavy lifting.

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 resource and scope: full UK tariff detail for one 10-digit commodity code. This distinguishes it from siblings such as uktariff_search and uktariff_heading, which operate at different granularity, without needing to name them explicitly.

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?

Provides clear example use cases such as 'what duty do I pay importing X into the UK' and 'is there a preferential rate from country Y'. However, it does not explicitly name alternative tools or state when not to use this tool.

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