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

No annotations are supplied, so the description carries the full burden. It does add real context beyond the schema — the 20-postcode cap (absent from the array schema, which has no maxItems) and the returned metrics — but omits auth/token requirements, rate limits, error behavior, and what happens when the cap is exceeded.

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?

One tight sentence with the report purpose front-loaded and the output metrics named up front. The leading 'PRO.' fragment is unexplained noise, but the rest wastes nothing.

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 5-parameter, no-annotation, no-output-schema tool, the description adequately covers what comes back (cheapest station, saving per fill) but leaves the input side thin — no defaults for radius_miles or tank_litres, no auth guidance, and no handling for oversized postcode lists.

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 only 40%: fuel and access_token are described in-schema, while postcodes, tank_litres, and radius_miles are not. The description partially compensates by clarifying postcodes as depot/site locations with a 20-item limit and implying tank size via 'saving per fill', but radius_miles and tank_litres remain unexplained.

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 — a batch "Fleet report" over depot/site postcodes that returns the cheapest nearby station and the saving per fill vs local average. The batch/multi-site scope implicitly separates it from the single-location siblings (cheapest_fuel, fuel_search, area_benchmark), though none are named.

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?

Usage is only implied: 'up to 20 depot/site postcodes' signals this is the multi-site batch variant, but the description never says when to pick it over area_benchmark or cheapest_fuel, nor what to do above 20 postcodes or whether a subscription is required.

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