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

Annotations already declare readOnly, idempotent, non-destructive, and open-world behavior. The description adds genuinely useful context beyond that: what is returned (OCR fields, registry fields, comparison results, resolved values), an explicit scope limit (phone numbers are not registry-compared), and the pricing model ($0.03 USDC per successful call via x402 on Base). It does not cover failure behavior or what happens on a mismatch, so it is strong but not exhaustive.

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 text is front-loaded with the core action, then cleanly labeled sections for usage, return values, and price. The full English/Japanese duplication doubles the length, but that is a deliberate localization choice rather than padding. Every English sentence carries information.

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?

There is no output schema, so the 'Returns:' enumeration is doing real work by telling the agent what comes back. Combined with the pricing and the phone-number exclusion, an agent has enough to call this correctly and interpret the result. It stops short of describing error or non-match behavior, which matters for a verification tool.

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 0%, so the description has to carry parameter meaning. It effectively explains registration_number, supplier_name, and address by describing the comparison it performs. It never mentions response_language or that address and supplier_name are optional, so it only partially compensates for the absent schema descriptions.

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 and resource: verify a T-number and compare issuer name and address against Japan's NTA registries. That is concrete and actionable. It does not, however, distinguish itself from close siblings like jp_invoice_registration_verify or jp_company_verify, so an agent cannot tell from the text alone which one to pick.

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 'Use when:' line gives a clear precondition: extracted issuer fields needing T-number, company-name, and address comparison. That is enough context to know when it applies. There is no explicit exclusion or routing to an alternative sibling tool, which keeps it 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.