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

With no annotations, the description carries the full burden and does well: it discloses the data source (資源エネルギー庁の週次調査・暮らしグラム), the tax rule basis (国税庁 No.2585・令和8年4月1日現在), that km must be supplied by the caller, and the 1.2–1.4 straight-line-to-road caveat. It does not state auth needs or error behavior, so not a 5.

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 purpose and returns, followed by routing examples and reference URLs. The list of example queries is somewhat long but each maps to a distinct use case; structure is functional with little filler.

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 an 8-parameter tool with no annotations and no output schema, the description explains what is returned (period totals, per-km cost, non-taxable commuter limit) and the provenance of the price data. Only permission/error behavior and the distinction from other cost tools are left unstated.

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%, so the schema already documents all 8 parameters (fuel enums, pref codes, defaults, rate_per_km override). The description adds only the straight-line-distance caveat and the fact that km is caller-provided, so it does not go beyond the baseline for high-coverage schemas.

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?

Starts with a specific verb+resource (ガソリン代の計算) and enumerates exactly what it computes and returns (片道・往復・1か月・1年のガソリン代、1kmあたりの円、通勤手当の非課税限度額). An agent can tell what it does, though it never names a sibling or states how it differs from cost tools like seikatsuhi or cost_item.

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 concrete trigger phrases ('〇〇まで車で行くと…', '通勤のガソリン代', '通勤手当は月いくらまで非課税') that map user intents to this tool. Clear context for when to call, but no explicit when-not or named alternative among the many cost/price siblings.

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