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

Annotations already cover read-only, idempotent, and non-destructive behavior. The description adds meaningful context: data source (European Commission Weekly Oil Bulletin), weekly reporting cadence, and the fact that output includes tax-inclusive and tax-exclusive prices plus tax share. This goes beyond the annotations without contradicting them.

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 longer than average but every sentence earns its place: use case, output semantics, data source, and fuel list. It is front-loaded with the primary question it answers and contains no filler, though a slightly tighter wording could make it more scannable.

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?

There is no output schema, so the description carries the responsibility for explaining returns. It covers country-level ranking, price per litre with and without tax, and tax share, which is enough for an agent to invoke the tool correctly. It does not specify currency or exact field names, but those are minor gaps given the level of detail provided.

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 100%, so the baseline is 3. The description adds value by enumerating exact fuel identifiers (petrol_95, diesel, lpg, heating_oil, fuel_oil_low_sulphur, fuel_oil_high_sulphur) that the schema only partially lists and does not define as enums. It does not describe the other parameters, but those are well-covered in the schema.

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 states a specific verb and resource: comparing/ranking fuel prices across European countries for a single fuel in the same week. It also gives concrete example questions, making the purpose immediately recognizable and distinguishable from sibling tools like fuel_price or fuel_price_history.

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 clear usage context: answering cross-border fuel cost questions, ranking countries, and comparing tax vs. underlying price. It does not explicitly name alternatives or state when not to use this tool, but the guidance is strong enough that an agent can infer when it is appropriate.

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