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

Annotations already declare readOnly/non-destructive/local-world behavior, so the safety profile is covered. The description adds genuinely non-structured context: prices are in ¢/L, results are capped at 10 stations within 30 km, and the precise definition of the 'value' sort (price + 1¢/L-per-km detour penalty). It does not mention rate limits or what fields are returned, but for a read-only lookup this is solid.

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?

Front-loaded with the core action, then scope caps, then the alternative-tool routing, all in three dense sentences with no filler. Slightly packed (the formula parenthetical and the routing clause both compete for attention), but every clause carries information.

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 six-parameter read-only lookup with no output schema, the description covers scope, units, result caps, default ranking, and sibling routing — enough for correct invocation. The only real gap is that it never hints at the shape of the returned station data, which an agent may need to plan a follow-up call.

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 67%, and the description fills the most important gap: the 'value' enum has no schema description, yet the description defines its formula and calls it the default, which materially affects how an agent sets `sort`. It also clarifies price units. It does not add anything for `limit`, `radius_km`, or `lat`/`lng` beyond what the schema already says.

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+resource+scope ('Find gas stations near a coordinate in Quebec') and the ranking modes, and explicitly names the sibling it is not ('for area-wide summaries use get_city_prices instead'), so an agent can distinguish it from get_city_prices without opening any schema.

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?

Gives an explicit use case ('sized for one fill-up decision'), an explicit exclusion with the alternative tool for area-wide needs, and even recommends the default ranking mode ('value ... the best default for "where should I fill up"'). When/when-not/routing are all covered.

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