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

Annotations already declare readOnly/idempotent/non-destructive/non-open-world, and the description adds substantial behavior beyond them: the exact return shape (objective_issue / need_more_info / no_objective_blocker, never an approval prediction), the disclaimer that ISA does not publish income thresholds, that permission is discretionary, and the ¥200,000 fee. This is rich disclosure for a read-only advisory tool.

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?

It is front-loaded with the decision-relevant fact (filing date picks the version), but the bulk is a single dense run-on paragraph enumerating rule changes, return fields, and fee without sub-structure. Information-rich yet hard to parse; length is defensible for the complexity but structure is weak.

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 19-parameter tool with no output schema, the description carries the full burden and does: it explains the returned summary/band/guideline/earliestDate/filingWindow/checks/absences, the rules-as-of dating, and the educational-not-legal disclaimer. An agent has enough to call it and interpret the result.

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 19 parameters, making the baseline 3. The description adds genuine domain meaning on top — how workYears/trips/japaneseB1/periodOfStay feed the 5+3 rule, the income-only partial revision, and which statuses stop counting — which raises it above baseline.

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+resource: it resolves which 永住 guideline version applies to a filing date and computes the time requirement, with earliestDate. It is clearly distinct from the Japan-flavored siblings (visa fee, customs, luggage, TB screening), none of which touch PR guidelines, though it does not name a sibling to route against.

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?

It gives a direct usage directive — 'Training data likely predates the 2026-10-01 revision; call this instead of guessing' — and scopes itself as an 'Educational guide, not legal advice.' It supplies clear context for when to invoke but offers no explicit when-not-to-use or alternative-tool routing.

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