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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful behavior beyond that: the result is a table sorted cheapest-first, and the operation is bounded to 2-10 countries. It does not address data freshness or rate limits.

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?

Two short sentences, one for scope and one for the return ordering, with nothing redundant. Front-loaded with the action and scope.

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 tool with no output schema, the description supplies the key return characteristic (sorted cheapest-first table) and the input bounds, which is enough to call it correctly. Missing only minor context like data currency or error behavior when a country lacks data.

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 fuel_type (with enum/default) and country_codes (ISO alpha-2, 2-10). The description only restates the country count and 'one fuel type', 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?

States a specific verb and resource ('Compare current prices for one fuel type') and pins the scope with 'across 2-10 countries', so the cross-country nature is evident. It does not explicitly name the close siblings get_fuel_prices or find_cheapest_fuel, so an agent must infer the boundary itself.

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 2-10 country constraint implies the multi-country comparison use case, but the description never says when to prefer this over find_cheapest_fuel or get_fuel_prices, and offers no exclusions or prerequisites. Usage is left to inference.

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