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

With no annotations provided, the description carries the full disclosure burden, and it does substantive work: it reveals handling of substitute holidays, 国民の休日, one-off imperial events, and the bank calendar's Dec 31-Jan 3 closure — behaviors un-inferable from the schema. It stops short of disclosing return shapes or out-of-range behavior, which keeps it from 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?

Two dense paragraphs with the core operations front-loaded; the later sentences justify edge-case coverage and the calendar default rather than repeating schema content. Each sentence earns its place, though the rhetorical 'awkward years' clause is slightly expansive.

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 four-operation tool with no output schema and no annotations, the description leaves the return side unspecified — what 'check' classifies a date as, what 'list' emits, and how count/shift results are shaped. The 'list' operation is absent from the prose entirely. Inputs are well covered, but the output side and per-operation behavior have clear gaps.

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%, so the baseline is 3, and the description need only add value beyond the schema. It does so for the least obvious parameter, 'calendar', explaining what 'bank' means (statutory calendar plus year-end closure) beyond the schema's bare 'Defaults to standard.' This is meaningful added semantics for exactly the parameter an agent would be unsure about.

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 first sentence names the resource (business days) with three specific verbs (count, shift, check), and the coverage statement (1955-2027) plus the calendar distinction pins down the tool's scope precisely. The prose omits the fourth operation 'list' (which appears only in the schema enum), a small completeness gap. No sibling tool performs date arithmetic, so differentiation is not a concern.

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 description gives concrete guidance for the main mode-selection decision: when to set calendar='bank', with a legal reference (銀行法施行令第5条) and a practical use case ('relevant for payment due dates'). It sets expectations about the covered year range (1955-2027), which implicitly bounds applicability. No sibling tools are named, but the sibling set is entirely monetary/payroll calculations, so there are no real alternatives to route between.

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