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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds the behavioral context that it mirrors the site's import duty calculator arithmetic, which is useful. It does not disclose details like rounding, currency conversion assumptions, or whether the estimate is binding, but with annotations covering the read-only nature, a 3 is appropriate.

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?

A single sentence that front-loads the core purpose and the key constraint (from China, same arithmetic as the site calculator). No wasted words; every part earns 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?

For a read-only estimation tool with 100% schema coverage and no output schema, the description is nearly complete. It could mention that the result is an estimate and not a binding quote, but the annotations and schema already cover the safety profile and parameters. The cross-reference to find_duty_rate helps the agent chain tools 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 schema already documents all five parameters. The description adds the context that duty_percent comes from find_duty_rate, which is a useful cross-reference, but it does not add meaning beyond the schema for the other parameters. Baseline 3 is correct.

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 ('Estimate') and resource ('customs value, UK import duty, import VAT and the total'), and distinguishes it from siblings by specifying the origin ('from China') and the arithmetic parity with the site's import duty calculator. It clearly differentiates from find_duty_rate and other sibling tools.

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 description implies when to use this tool: when estimating landed cost for imports from China, and the schema references find_duty_rate as the source for duty_percent, which gives a clear context. However, it does not explicitly state when not to use it or name alternatives, so it falls 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.