find_cheapest_fuel

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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint, so the safety profile is covered. The description adds valuable behavioral context beyond that: a hard radius cap of 25 km, a station cap of 10, that prices over an hour old are flagged, and that the attribution line and MTS-K note must be shown. These are concrete operational constraints that materially affect how an agent uses the 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?

The description is two sentences of core purpose and guidance followed by constraints, all front-loaded with the most important information first. There is no filler or repetition of schema details; every sentence adds unique value, making it dense but efficient.

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?

Despite having no output schema, the description outlines what the result contains (price, brand, address, distance, open state, price age) and notes the attribution requirement. All operational constraints (radius, limit, language) are covered, and the parameter schema is fully documented. An agent has everything needed to call the tool correctly and interpret the response.

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% with thorough per-parameter explanations, so the baseline is 3. The description adds practical selection guidance that goes beyond the schema: it emphasizes matching the fuel grade to the driver's vehicle ('a diesel driver is not helped by a petrol price') and mandates setting the language to the user's language to avoid wrong-language answers. These enrich the meaning of the fuel and language parameters beyond their basic descriptions.

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 opens with a specific verb and resource: 'Returns the cheapest petrol stations for one fuel grade around a place or coordinate,' and lists the exact data fields (price per litre, brand, address, distance, open state). It also differentiates from siblings by explicitly excluding charging and traffic use cases, making its scope unambiguous.

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 provides explicit when-to-use guidance ('Use when the user asks where to fill up, what fuel costs nearby, or for a cheap stop on a drive') and when-not-to-use guidance with named alternatives ('Do NOT use for charging an electric car (call find_charging_station)... for motorway traffic (call check_autobahn_traffic)'). This leaves no inference needed.

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