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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description goes further by disclosing the actual deliverables — official prices plus a service fee in EUR, non-vignette tolls, and a pre-filled order link — which matters because there is no output schema. It does not discuss coverage limits, whether some countries lack vignettes, or result freshness.

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 densely packed sentence that lists outputs in a logical order, with the core product (vignettes needed) front-loaded ahead of supporting details like prices and the order link. It is long but every clause carries information; only the trailing order-link clause could be trimmed.

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?

Five parameters, no output schema, and no nested objects — the description compensates for the missing output schema by enumerating exactly what comes back (products, prices with service fee, tolls, order link). Combined with full schema coverage and clear annotations, an agent has what it needs to call this correctly, though vehicle-class scope and country coverage limits remain unstated.

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% and all five parameters carry their own descriptions (defaults for start/end, enum for lang, city-or-country-code for from/to), so the schema does the heavy lifting. The description only reinforces the from/to semantics with 'between two places' and hints at dates via 'covering the dates in each country', adding no syntax or format detail beyond the schema. Baseline 3 applies.

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 names a specific resource and scope: motorway vignettes required for a passenger-car trip between two European places, plus the ancillary outputs (cheapest product per country, prices in EUR, non-vignette tolls, pre-filled order link). It is a noun-phrase output inventory rather than a verb+resource statement, but an agent understands immediately what it yields and can distinguish it from the static list_cities / list_vignette_countries siblings.

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 only implied: 'between two places in Europe' and 'passenger-car trip' scope it, and the presence of 'from'/'to' shows it is route-specific rather than a lookup. There is no explicit when-to-use statement, no exclusion (e.g. no mention that this is car-only vs. other vehicle classes), and no routing to the sibling list tools for exploring supported countries or cities.

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