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

Annotations only supply readOnlyHint=true, so the description carries the rest — and it does useful work by naming the authoritative source (annual securities report), warning that share counts are in trading units rather than shares, and specifying that ratios are 0–1 decimals. That unit caveat is exactly the kind of trap an agent would otherwise fall into when presenting the numbers.

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 core sentence is well front-loaded and information-dense. However, the ISO 8601 date-time boilerplate is restated in both English and Japanese and is largely irrelevant to a tool with no date-time parameters or documented date outputs, which roughly doubles the text for no added decision value.

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?

With only two parameters, one required, full schema coverage, and read-only semantics, the description is nearly self-sufficient; because there is no output schema it also usefully enumerates the returned fields per category. Minor gaps remain around whether multiple fiscal years can be requested and what a missing report yields.

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 symbol and fiscalPeriod are already documented with format and an example. The description adds nothing about fiscalPeriod's semantics or behavior (e.g., what happens when no report exists for the requested period), so it sits at the 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?

States a specific verb and resource — ownership broken down by shareholder type from the annual securities report — and enumerates the exact categories returned (governments, financial institutions, securities firms, other corporations, foreign investors, individuals). This implicitly separates it from holder-level siblings like get_major_shareholders and get_large_holders, but it never names them explicitly.

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 'from the annual securities report' phrasing and the parameter note 'Omit for the latest annual report' imply the usage context without stating it as a rule. There is no explicit guidance on when to pick this over get_major_shareholders, get_cross_shareholdings, or get_treasury_shares, all of which live in adjacent territory.

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