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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered; the description goes further by disclosing the deterministic rate table (€5 for one power bank, free for 2–5, case free with a power bank or €2 alone) and the country-invariance rule. It also states what is returned (an exact EUR cost), useful given no output schema. Only gaps are rounding/tax/format details.

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 front-loaded sentence: the resource and unit come first, then the rate table in parentheses, then the country scope note. Every clause carries operational information; nothing is redundant.

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 three-optional-parameter read-only calculator with no output schema, the description covers purpose, computation, currency, and return type. Minor omission: it does not say how an empty basket or a zero-cost result is represented, but that is a small residual gap for this complexity.

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 100%, so the baseline is 3, but the description adds real meaning the schema cannot: the interaction between `cases` and `power_banks` (a case is free only when a power bank is present). That interaction is not derivable from the two independent integer fields alone.

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 verb and resource — 'Exact shipping cost in EUR for a basket' — plus the exact pricing rule that governs the result. It is unmistakably distinct from the sibling tools (compatibility, product details, policies, search), so an agent can route to it without ambiguity.

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?

Use is implied by the phrasing (call it when you need a basket's shipping cost) but there is no explicit when-to-use or when-not-to-use statement, and no alternative tool is named. The line 'Same rate for every country' usefully signals that country need not be supplied, which is a partial usage constraint.

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