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

Annotations declare readOnlyHint=false, idempotentHint=true, destructiveHint=false, openWorldHint=true. The description adds valuable behavioral context: deterministic results, cites primary sources, errors and unverified rules are never billed, and the $0.01/call pricing. It also discloses the x_payment behavior implicitly through the schema. This goes beyond 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?

Three sentences with zero waste. The core purpose is front-loaded, pricing is stated, and the deterministic/source-citing behavior is compressed into a single clause. Every sentence earns its place.

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 tool with 5 parameters, full schema coverage, and no output schema, the description is quite complete. It explains the source, the pricing, the deterministic behavior, and the payment flow. The only gap is that it doesn't describe the return value shape, but with no output schema and a clear domain (premiums), an agent can infer the result. A 4 is fair.

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 5 parameters. The description adds context about the grade table lookup and the payment scheme (x_payment) that helps an agent understand the billing behavior. It doesn't add much per-parameter detail beyond the schema, but the baseline is 3 with full coverage, and the description's mention of the grade table and payment requirements adds meaningful context.

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 ('calculates' implied by 'Monthly social insurance premiums'), a precise resource (official Kyokai-Kenpo grade table FY2026), and a distinguishing scope (monthly premiums). It clearly differentiates from siblings like jp_bonus_net, jp_payroll_net, and jp_consumption_tax by naming the exact source table and period.

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 implies when to use it: when monthly social insurance premiums are needed from the official grade table. It doesn't explicitly name alternatives or exclusions, but the specificity of 'monthly social insurance premiums' and 'official Kyokai-Kenpo grade table' gives clear context. A 4 is appropriate because it lacks explicit when-not-to-use guidance but is otherwise clear.

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