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

With no annotations, the description carries the full burden, and it does disclose useful traits: the call is free, the search radius is fixed at 5 miles, exactly 3 results are returned, and prices are in pence per litre. It omits auth/prerequisite needs, the behavior when fewer than 3 stations exist, and whether the radius is configurable.

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 tight fragments with the strongest hook ('FREE') front-loaded and zero filler. Slightly telegraphic phrasing, but every element 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 a simple two-parameter lookup with no output schema and no annotations, the description covers the essentials (result count, radius, unit). It stops short of covering the omitted-fuel default and the empty-result case, which an agent would need to call it confidently.

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 50%: 'fuel' is documented in the schema with its four grade codes, but 'postcode' has no description. The description adds the price unit and confirms postcode scoping, but does not explain the optional 'fuel' parameter's default when omitted, which is the main semantic gap.

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 (cheapest 3 UK fuel stations), a concrete scope (within 5 miles of a postcode) and the unit (pence per litre). It is clear what the tool returns, though it never contrasts itself with the sibling fuel_search or area_benchmark.

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?

There is no when-to-use or when-not-to-use guidance and no mention of fuel_search, which by name appears to overlap heavily. The only routing hint is the word 'FREE', which implies a cost tradeoff but never names the alternative.

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