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

Annotations already cover the safety profile (readOnly, idempotent, closed-world, non-destructive), yet the description still adds real value: it declares that holiday-data failure is a hard error rather than a silent weekday-only result, and it discloses the computational bound of 10 API requests of up to 11 years each plus one retry. That error-semantics and rate/bound disclosure is exactly what an agent needs before committing to a large date range; only the return payload detail is thin, and an output schema exists.

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 operation and its scoping defaults are front-loaded, and every later sentence carries distinct information: weekend configuration, error policy, return contents, and request bounds. Slightly dense and the final parenthetical about retries is awkwardly nested, but nothing is filler.

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 8-parameter tool with an output schema, the description covers defaults, error behavior, and computational limits, and the schema covers parameter formats and enums. The only real gap is the absence of explicit routing guidance among the three sibling date/holiday tools.

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 75%, so the baseline is 3. The description restates the defaults (no excluded weekdays, no holidays, later endpoint excluded) and gives one practical mapping ('[0,6] for weekends'), but that largely duplicates enum/pattern/default metadata already present in the schema and adds no guidance on the country/region dependency beyond what the schema states.

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 opening sentence names a specific verb and resource ('Count calendar or matching days between two Gregorian dates') and pins the semantics with a reference implementation. An agent can distinguish it from shift_date (which moves a date) and get_holidays (which lists them), though siblings are never named 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?

Usage is implied through defaults and configuration hints ('Use excludeWeekdays [0,6] for weekends'), which tells the agent how to get a business-day count. However, there is no explicit when-to-use vs shift_date/get_holidays guidance and no statement of when this tool should not be chosen.

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