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

The annotations (readOnlyHint true, destructiveHint false) already establish that the tool is a safe read-only calculation. The description adds context the annotations do not: which days are excluded from the business-day count (weekends, holidays, closed weekdays, Obon, New Year, individual closures and openings), and which counting rules apply. It does not describe the response shape or ordering.

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?

Three sentences with the core purpose stated first, followed by the counting rules and then the edge-case semantics. The final sentence is dense and convoluted, and some of the content simply restates the per-parameter documentation in the input schema, but overall it reads cleanly and stays on topic.

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 an 11-parameter tool with complex holiday logic and no output schema, the description explains the inputs well but never says what the tool returns. The caller has to infer the response shape, presumably total days and business days, which is the biggest gap given that multiple counts look plausible.

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 the schema handles the bulk of the parameter documentation and the baseline score of 3 applies. The description goes slightly beyond the schema: it clarifies business_count_start (whose schema text is just one line) and explains the concrete effect of that flag, so it adds some semantic value.

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 verb (counting) and a specific resource (days and business days between two dates), and spells out the holiday/weekend rules that define the calculation. It does not differentiate itself from the available siblings such as check_business_day, add_days, or find_dates; its only pointer is to an external web tool (/tools/date-calculator).

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?

It gives one concrete usage recipe – counting the business days in a month by setting start to the 1st, end to the last day, and business_count_start: true – and says the counting rules match /tools/date-calculator. However, it never says when to choose this tool over check_business_day or add_days, and it never states when this tool is not appropriate.

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