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

Annotations already indicate read-only, idempotent, and non-destructive behavior. The description adds valuable context that the estimates are approximate, the cashback expected value is not a measured rate, and that final conditions must be verified on official sites. 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 front-loaded with the core purpose and formula, followed by important disclaimers. It is slightly verbose but every sentence contributes useful information, so it earns a 4 rather than a 5.

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?

The description explains what the tool returns (sorted plans, effective total, cashback expected value, and total if not received) and includes necessary caveats. Given no output schema, this is sufficient for an agent to understand the tool’s behavior and output, though it leaves some details to the schema.

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 each parameter already has a clear description. The tool description adds the overarching cost formula but does not provide additional detail for individual parameters beyond the schema, making the baseline score of 3 appropriate.

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 clearly states that the tool searches optical line plans (光回線プラン) by building type, mobile carrier, and number of lines, and sorts them by effective total cost using a specific formula. This specificity distinguishes it from generic siblings like search_plans and compare_hikari_plans.

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 gives clear context for when to use the tool (searching optical line plans with specific criteria) and includes caveats about final verification. However, it does not explicitly mention alternatives or exclusion cases, so it falls slightly short of a 5.

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