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

With only readOnlyHint supplied, the description does real work: it identifies the source document (有価証券報告書), states the voting-rights ratio is on a 0–1 scale, and gives date/time conventions including the JST offset. It also sketches what each returned row contains, which matters since there is no output schema; it stops short of saying what happens when no subsidiaries are reported or how large the result set can be.

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 purpose statement is front-loaded and information-dense, but the entire body is duplicated in Japanese, roughly doubling length without adding information for a single reader, and the date-format boilerplate sits at the end where it reads as generic filler.

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 two-parameter read tool with no output schema, the description covers source, scope, returned fields, and value conventions well enough to invoke it confidently. Residual gaps (empty-result behavior, coverage limits) are minor.

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 both parameters are already fully documented, including the ticker format and the 'omit for latest' default. The description adds no parameter-level meaning beyond that, 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 (group structure from the annual securities report) and enumerates its scope precisely: parent, consolidated subsidiaries, equity-method affiliates, and other related companies. The field list (address, capital, main business, voting-rights ratio, relationship) makes it clearly distinct from siblings like get_cross_shareholdings or get_major_shareholders.

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 implied by the stated data source ('from the annual securities report') and by the schema note that omitting fiscalPeriod returns the latest report, but the description never says when to choose this over get_cross_shareholdings or get_major_shareholders, nor any preconditions (e.g., only companies that file a securities report).

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