fuel_area_summary

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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=true, and destructiveHint=false, so the safety profile is covered by metadata. The description adds value by disclosing the aggregation behavior (statistics per fuel type) and the analytical intent (judging price competitiveness), which goes beyond the structured metadata. It doesn't discuss potential rate limits, data freshness/coverage limitations, or what happens for areas with no stations, but it doesn't contradict annotations.

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?

Two concise sentences with zero filler. The first sentence states the core functionality with specific outputs (min/median/max, cheapest station), and the second adds practical usage guidance. Every sentence earns its place and the description is appropriately front-loaded.

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 an output schema present, the description doesn't need to explain return values. The description covers the aggregation purpose, the location parameter context, and the analytical use case. Given it's a relatively simple two-parameter read-only aggregation tool with good annotations and output schema, the description is essentially complete; minor gaps around data coverage limitations or radius semantics prevent 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 50%: the 'location' param is described ('UK postcode, outcode or lat,lon') but 'radius_miles' has no description. The tool description adds some context by indicating the area scope concept, but neither the description nor the schema clarifies radius_miles semantics beyond its default (10) and range. With partial schema coverage, the description partially compensates but doesn't fully cover the undocumented parameter.

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 clearly states the verb+resource+scope: 'Per-fuel price statistics for an area: min/median/max and the cheapest station for each fuel.' It specifies exactly what outputs (statistics and cheapest station) and clearly distinguishes itself from siblings like fuel_find_cheapest (which finds a single cheapest) and fuel_nearby_stations (which lists stations). It even frames its purpose relative to a user need ('judge whether a price you've seen is actually good locally').

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 gives clear usage context ('Use it to judge whether a price you've seen is actually good locally'), which effectively communicates when to use this aggregation tool versus alternatives. It doesn't explicitly state when NOT to use it or name sibling alternatives, but the purpose statement strongly implies the appropriate use case relative to the sibling tools.

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