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

Beyond the readOnlyHint/idempotentHint annotations, the description discloses what the response contains (price incl/excl tax, tax share, week), that the figure is a national average reported weekly by EU Member States, and that it covers 28 countries. This materially helps an agent interpret the result and set expectations.

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?

The description is long but every sentence earns its place: front-loaded purpose, example queries, return composition, data provenance, and fuel list. No filler or redundancy.

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 fully explains the return values (price including and excluding tax, tax share, week) and contextualizes the data source. It also clarifies the fuel scope and country resolution, making the tool safe to invoke for an agent with no further lookups.

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?

The input schema already covers all three parameters with 100% description coverage, giving a baseline of 3. The tool description adds meaningful parameter semantics by stating the default fuel, forgiving fuel synonyms ('gas', 'gasoline', 'autogas'), and how country codes and 'EU' work, going beyond the schema strings.

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 pair ('current pump price per litre for petrol, diesel or LPG') and grounds it with concrete example queries. It is clearly distinct from sibling tools like fuel_price_history and compare_fuel_prices by emphasizing 'right now' and the weekly national-average scope.

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 description conveys strong contextual use cases ('how much is petrol in Portugal') and clarifies the data is a weekly national average rather than a station price. It does not explicitly name sibling alternatives or state when not to use this tool, but the 'right now' framing and examples make the intended usage clear.

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