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

Annotations supply only readOnlyHint, so the description carries most of the burden and does it well: it discloses the 404 outcome for missing reports, the empty result for foreign-format filers (naming 9399 as the current example), and ISO 8601 UTC formatting for dates with a +9h Japan-time note. It does not describe response envelope or pagination, but for a single-object read that is a minor omission.

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?

Content is front-loaded and each clause carries real information, but the entire description is duplicated in English and Japanese, roughly doubling length. The trailing ISO 8601 date-format paragraph is also largely irrelevant to the two input parameters and reads as boilerplate.

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 no output schema, the description must name return values, and it does enumerate the core fields plus the segment breakdown and the empty-result case. It stops short of describing the shape of the returned object (nesting of segment rows, units beyond JPY for salary), which is the one remaining gap for a no-output-schema 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 coverage is 100%: symbol (4-digit ticker) and fiscalPeriod (YYYY-MM, omit for latest) are both documented in the schema, and the description adds no syntax or constraint beyond that. Per the baseline rule, a 3 is correct when the schema does the heavy lifting.

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?

Names the resource and the exact report it comes from (latest annual securities report) and enumerates the fields returned: headcount, average age, average years of service, average annual salary in JPY, and consolidated employees by segment. It explicitly distinguishes itself from the sibling get_employee_count, so an agent can choose between them without opening schemas.

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 concrete selection context: foreign-company-format reports (jpcrp080000) have no employees section, and a company with no annual securities report gets a 404 here while get_employee_count returns employeeCount: null. That effectively routes the agent between the two tools, but it is framed as behavior rather than explicit 'use X when Y' guidance, and there is no statement about when to prefer fiscalPeriod over the latest report beyond the schema default.

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