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

Annotations already declare readOnly, idempotent, non-destructive and openWorld, so the safety profile is covered. The description adds useful scope behavior: coverage across all API-supported countries, the full fuel-type set, and that omitting country_code downgrades the response to a summary list. It says nothing about data freshness beyond 'current' or rate limits, so it is not a 5.

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?

Front-loaded with the resource, then the fuel coverage, then the parameter behavior. The final sentence largely repeats the country_code behavior already stated one sentence earlier, which is mild redundancy, though the petrol/gasoline/autogas synonyms add value for query matching.

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?

An output schema exists, so return values need not be explained, and the description covers scope, fuel types, and both operating modes. The main gap is that it never routes the agent away from the closely related compare_fuel_prices and find_cheapest_fuel siblings, which are the most likely mis-selection candidates.

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 both locale and country_code in detail. The description's 'Pass country_code to get one country in detail; omit it for a summary list' restates what the schema field description already says, and it ignores locale entirely. Baseline 3 applies when the schema does the heavy lifting.

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 ('Current retail fuel prices') and enumerates the covered fuel types, so the agent knows exactly what data comes back. It also distinguishes the two operating modes (single country vs. overview). It stops short of naming the directly competing siblings (compare_fuel_prices, find_cheapest_fuel), so an agent could still pick the wrong fuel tool.

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?

Gives explicit when-to-use context: 'Use it for the price of petrol, diesel, LPG/autogas/propane or CNG in one country; without a country it gives an overview.' This maps intent (single price vs. overview) to the presence of country_code. No exclusions or named alternatives are given, so it does not reach a 5.

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