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

No annotations are provided, so the description carries the full burden, and it does disclose key behavior: the result is capped at 20 nearby stations and prices are in local currency per liter/kWh. It stops short of stating data freshness/latency, station coverage limits in rural areas, or error behavior for unknown postcodes, which are the remaining traits an agent would want for a live-data tool.

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 core capability, then the usage condition, then the exclusion, then the return shape. The second sentence largely re-lists the fuel types already named in the first sentence (petrol 95/98, diesel, LPG, EV DC), which is mild redundancy but adds the octane detail.

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 2-parameter tool with no annotations and no output schema, the description covers purpose, exclusions, and the essential shape of the response (up to 20 stations, local currency, per liter/kWh). Missing only freshness expectations and failure modes for unmatched locations, which keeps it short of a 5.

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%, and the schema already documents the ISO 3166-1 alpha-2 format for country_code and the postcode/ZIP/city form for postal_or_city. The description only restates 'by country and postcode/city' and adds no new constraints such as how to disambiguate a city name shared across regions. 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?

States a specific resource (live petrol, diesel, LPG and EV fast-charging retail prices) and a specific lookup dimension (postcode or city). It also explicitly distinguishes itself from getCommodityPrices, so an agent can separate it from the commodity-pricing sibling without opening either 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 explicit when-to-use guidance ('looking up retail pump prices ... at local stations by country and postcode/city') and an explicit when-not-to-use clause pointing at the named alternative getCommodityPrices for wholesale crude or futures. Nothing about tool selection is left to inference.

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