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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description goes well beyond by disclosing currency behavior (Canada charged in CAD at a fixed rate, with charged.amountCents reflecting the actual charge), the shape of the returned figures, and an explicit failure mode listing unsupported destinations (South Korea, sanctioned countries). This is exactly the kind of behavioral context annotations cannot express.

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 dense, front-loaded sentences with no filler — the core cost definition comes first, then currency behavior, then the failure case. The middle sentence is slightly garbled ('at a fixed rate; charged.amountCents shows that'), a minor readability cost but not enough to derail an agent.

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?

With no output schema, the description carries the return-value burden and does so by naming the returned components and the failure payload (supported:false with a message). Combined with the destination restrictions and currency handling, an agent has everything needed to call this correctly and interpret the result.

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 67%, and the description adds genuinely new semantics the schema lacks: which destinations are unsupported at all (South Korea, sanctioned countries) and the CAD fixed-rate charging behavior. It also restates the 10-product cap already in the schema's maxItems and says nothing about the quantities array, so it does not fully close the coverage gap.

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 and resource — the delivered (landed) cost for up to 10 products to one destination — and enumerates the components (items, shipping, duties estimate, tax, DDP total in USD cents). The phrase 'the same numbers the store's own checkout charges' implicitly separates it from nodajimarket_create_checkout, which actually places the order, so an agent can distinguish the estimate tool from the mutation sibling.

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?

Usage is implied rather than stated: the agent can infer this is a pre-purchase estimate versus create_checkout, but the description never explicitly says 'call this before checkout' or names alternatives. It does give one exclusion — unsupported destinations return supported:false — which is a failure condition rather than routing guidance.

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