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

With no annotations, the description carries the burden and does so well: it discloses that negativeInterests/remainingHistories need individually-managed per-stock data, that missing data surfaces a reason in notes, that basic-only avoids fetching heavy data, and it mandates a user-facing disclaimer that 逆日歩 is past data and not predictive. It omits auth/rate-limit/error behavior, so not a 5.

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?

Front-loads the one-line purpose before a well-structured bulleted breakdown of sections. The section bullets are dense but each earns its place given the market-specific terminology (vestingDates, karaDates, systemLendingStatus values); 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 2-param tool with an output schema, the description covers everything an agent needs: default behavior, all section semantics, data-availability caveats and the notes fallback, performance characteristics, and a required disclaimer. No material gap remains.

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 coverage is 100% and the schema already documents both code and sections (including the default and example combinations), so baseline 3 applies. The description's deep per-section content breakdown largely duplicates return-value detail, which an output schema already exists to convey.

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+resource+scope: "銘柄コードで株主優待を1件取得する" — a single-record fetch by stock code. It is clearly distinct in intent from the search-oriented sibling search_benefits, though it never names a sibling explicitly to force that contrast.

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?

Gives clear per-section guidance on what each value returns and when to request it (e.g. "逆日歩履歴が欲しいときは [\"basic\",\"negativeInterests\"]"), plus the default (basic) and the lightweight fallback. No explicit when-not or sibling routing (e.g. vs search_benefits), so it stops short of 5.

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