fuel_prices

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

No annotations, so the description carries the full burden and does well: it discloses sort order (cheapest first), data source (official DGEG), price units (per litre vs per kg/m3 for gas), the last_update freshness field, and the instruction to always cite source and update time. It stops short of stating read-only character, caching/update cadence, or failure behavior.

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 one-line summary followed by a usable Args block and a short returns paragraph. The "Each station: ..." enumeration partly duplicates the output schema, but the closing instruction to always cite DGEG and last_update earns its place.

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 an 8-parameter, annotation-free lookup tool this is essentially complete: input forms, defaults, geographic precedence, units, ordering, provenance, and the sibling that enumerates legal fuel_type values. Return details being duplicated is harmless given an output schema exists.

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 0%, so the description must compensate and it does for all eight parameters: fuel_type accepts DGEG names, numeric ids, or plain words like "diesel"/"lpg"; district vs municipality with precedence; lat/lon triggering distance_km within radius_km; brand as a substring match; limit default 10 max 50. It also notes case/accent-insensitive name matching, which the schema cannot express.

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?

Names a specific resource and operation (cheapest fuel stations in Portugal, cheapest first, DGEG source) and distinguishes scope from siblings by directing agents to fuel_types() for the full fuel list. An agent can tell this is the search-a-price tool, not the detail tool, without opening the schema.

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 concrete trigger phrasings ("where is diesel cheapest in Lisboa / near me / in Braga") and states the default when no area is given (searches all of Portugal), plus the municipality-overrides-district rule. It doesn't explicitly say when to prefer fuel_station_detail or fuel_types instead, so routing is implied rather than fully enumerated.

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