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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds real behavioral context the annotations cannot: savings are point-in-time estimates tied to captured_at and saving_basis, and cross-border offers carry EU warranty and returns but possible foreign-language support. It does not mention pagination or default limit 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 in the first clause, and each subsequent clause adds non-redundant information (saving semantics, estimate caveat, cross-border caveats, sibling pointer). The nested parentheticals and backtick field references make it dense to parse, costing a point on readability.

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 list tool with no output schema, the description names the fields an agent will encounter (saving_kind, saving_basis, captured_at) and explains what a returned row represents. What is missing is result-size/pagination behavior tied to the limit parameter, which an agent would want before calling.

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%, with locale and deliver_to_country already documented in the schema. The description reinforces deliver_to_country by explaining the saving is expressed in that currency, but it says nothing about the limit parameter or default result counts. That is the expected baseline when the schema does most of the work.

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 gives a specific verb-and-resource definition: products whose cheapest total (goods + shipping + FX) comes from an abroad shop and beats the cheapest domestic offer. It explicitly differentiates itself from find_best_price, which shows the cross-border block for a single product, so an agent can pick between the two without opening either schema.

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 final clause ('find_best_price shows the cross_border block for one product') implicitly routes the agent: use this for a bulk/list view, find_best_price for one product. It also gives presentation guidance ('present it as an estimate, never a guaranteed result'). There is no explicit 'when not to use' or prerequisite statement, 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.