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 fully covered. The description adds the price-key coverage (gasoline, diesel, LPG, etc.) but says nothing about rate limits, data freshness, units, or currency of the returned prices.

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?

Three sentences, front-loaded with the core resource statement, and the invocation rule comes last in a natural place. The enumerated fuel-key list is mildly verbose but earns its place as coverage information.

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?

With no output schema, the description carries the burden of describing the return shape, and it only partially does so — it hints at 'summary list' vs 'in detail' and names price keys but never explains the structure, units, or currency of returned prices. Adequate but with a clear gap for a data-retrieval tool.

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% and the single parameter is already documented with its ISO format and omit behavior, so baseline is 3. The description's 'one country in detail' phrasing adds a small nuance about response granularity beyond the schema's 'returns all countries', but no real parameter syntax detail.

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 verb+resource ('Current retail fuel prices') and states the scope ('all API-supported countries'), which distinguishes it from the more targeted siblings compare_fuel_prices and find_cheapest_fuel. It stops short of naming those siblings explicitly, so it is clear but not fully disambiguating.

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?

It gives an explicit conditional: pass country_code for one country in detail, omit it for a summary list. That is clear invocation context, though it never states when to prefer this tool over compare_fuel_prices or find_cheapest_fuel.

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