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

Annotations already cover the safety profile (readOnly, idempotent, openWorld), and the description adds real context on top: closure data appears only when the source states it, status_as_of is derived from gBizINFO's last_acquisition_date, the response carries a gBizINFO source notice, and the result is explicitly not official. It does not contradict any annotation.

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 scope of returned data is front-loaded in the first clause, followed by provenance and disclaimer notes in a compact form. Slightly awkward question-form opening and a few clauses that restate provenance (source notice / not official) cost it the top score, but nothing is padded.

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 single-parameter read tool with a full output schema and covering annotations, the description supplies what structured fields cannot: data provenance (National Tax Agency via gBizINFO), conditional presence of closure data, the meaning of status_as_of, and a not-official caveat. An agent can call and correctly interpret the response without further context.

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 sole corporate_number parameter is fully documented (format, example, check-digit validation) without description help. The description only refers to it obliquely as 'this Japanese corporate number', adding nothing beyond the schema, so the 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 (basic information for a Japanese corporate number) and enumerates exactly which fields come back (name, kana, English name, address, closure date/cause), plus an explicit exclusion (representative names are not returned). It distinguishes itself from gbizinfo_certifications by scoping to basic registry data, but never names gbizinfo_resolve_corporate_number as the way to obtain the number, so sibling differentiation is implicit rather than stated.

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?

Usage is only implied: the reader infers that a valid 13-digit corporate number is required and that this is the lookup for core registry facts. There is no explicit when-to-use statement, no condition for choosing it over catalog/gbizinfo_certifications, and no pointer to gbizinfo_resolve_corporate_number for name-to-number resolution.

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