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

Annotations already mark this as read-only, idempotent, and non-destructive, so the safety profile is covered without needing description. The description adds that results are ranked countries filtered by region/fuel type, but does not mention output shape, ordering guarantees, or edge cases such as fewer results than limit. This is adequate but not rich.

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, with the core capability front-loaded and a use case in the second sentence. Every word earns its place; no filler or repetition of schema details.

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 simple three-optional-parameter tool with full schema descriptions and safe annotations, the definition is nearly complete. The description indicates the result will be a set of cheapest countries, which is the key missing output information given there is no output schema. A slight gap is not specifying whether prices accompany the country results, but this is minor.

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%, including default values and enums, so the description does not need to restate parameter semantics. The description mentions fuel type and region but adds no meaning beyond the schema; limit is not referred to at all. Baseline 3 is appropriate.

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 uses a specific verb+resource: find the cheapest countries for a fuel type in a region. It is clearly not a generic price lookup, and 'countries' distinguishes it from siblings like get_fuel_prices. However, it never explicitly names or contrasts sibling tools, so it stops short of full differentiation.

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?

'Useful for route planning' gives an explicit context where this tool should be selected. It also clarifies the optional worldwide scope. It does not explicitly say when to choose get_fuel_prices or compare_fuel_prices instead, so it lacks an exclusion statement.

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