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

With annotations already declaring idempotentHint=true and destructiveHint=false, the description adds material context the annotations cannot: a per-call price ($0.01), deterministic results, primary-source citation, and a no-charge guarantee for errors or unverified rules. It does not explain the x402 payment handshake beyond what the x_payment schema field covers, which keeps it short of 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?

Two compact sentences, purpose front-loaded, followed by cost and reliability claims. Every clause carries information; the only slight redundancy is that billing behavior is partly repeated by the schema's x_payment field.

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?

An output schema exists, so return values need no prose, and annotations cover the safety profile. The description supplies cost, determinism, and sourcing, but omits the one thing an agent still needs: routing guidance versus the other jp_payroll* tools.

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 five parameters including age-gated care insurance and the as_of rules-version selection. The description's 'Kyokai-Kenpo grade table (FY2026)' and 'monthly premiums' only loosely gloss monthly_remuneration_yen and the rules version, so baseline 3 applies.

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 names a specific resource (monthly social insurance premiums) and its authoritative source (the official Kyokai-Kenpo grade table, FY2026), which is enough for an agent to tell it apart from jp_consumption_tax, jp_mortgage, or jp_payroll_net. It never states the verb explicitly ('calculates'), so it is clear rather than maximally precise.

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?

There is no guidance on when to choose this over siblings such as jp_payroll_net or jp_payroll_suite, nor any prerequisite or exclusion stated. The only selection signal is the implied 'Japan social insurance' domain carried by the name.

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