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

Annotations already declare readOnly, idempotent, and non-destructive hints. The description adds valuable behavioral context: estimates are approximate and may differ due to fuel adjustment, usage, and discount conditions; final terms must be verified on official websites; and affiliate compensation is disclosed. This goes well 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 well-structured: purpose in the first sentence, usage instruction in the second, and necessary disclaimers in a separate paragraph. Every sentence earns its place; the disclaimer could be slightly tighter but is legally and contextually necessary.

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?

Without an output schema, the description lists the key aspects covered by the comparison, supplies usage prerequisites, and includes accuracy caveats and affiliate disclosure. This gives an agent sufficient understanding of the tool's functionality and limitations.

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 baseline is 3. The description repeats the plan_ids source instruction already present in the schema but offers no new parameter semantics. All parameters are thoroughly described in the schema with defaults, enums, and constraints.

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 uses the specific verb '詳細比較します' (compares in detail) and enumerates the comparison dimensions: annual estimate, cancellation fees, fuel cost adjustment method, point rewards, and set discounts. This clearly differentiates it from siblings like search_plans and simulate_cost, establishing a unique purpose.

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 explicitly instructs that plan IDs should come from search_plans/simulate_cost results, providing a clear workflow. It does not explicitly state when not to use this tool versus alternatives, but the multi-plan comparison scope implicitly distinguishes it from single-plan simulation tools.

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