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

Adds genuinely new context beyond the annotations: per-call pricing, 25 free calls, failed calls free, and the warning that repeats are not free (consistent with idempotentHint=false). It also discloses the fallback behavior for unlisted countries. The 'reads or computes only and changes nothing' sentence largely restates readOnlyHint/destructiveHint, and return-field structure is only hinted at, keeping it out of the top band.

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-loaded with the core operation and both modes, then use cases, then an example, then pricing. Dense and mostly waste-free, though the pricing/commercial tail adds bulk that an agent making a first selection does not strictly need.

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 4-parameter computational tool with no output schema, the description covers both modes, the default for 'to', the country-calendar fallback, and the cost model. The only gap is the exact shape of the returned counts/holiday list, which it gestures at ('list the holidays skipped') without detail.

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 already 100%, so baseline would be 3; the description adds value by spelling out the country calendars with human-readable names (US, UK, Sweden, Germany, France, Norway, Denmark, Finland) that map onto the ISO codes in the schema, and by clarifying the add=N alternative including negative values. It still doesn't clarify how conflicting to/add inputs are resolved.

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 ('count business days between two dates') and covers both modes (count between dates, or add=N to shift a date) in the same breath. It is clearly distinguishable from date_diff/date_add siblings because it names the weekend-and-holiday skipping behavior and the country calendars.

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 use cases ('delivery estimates, SLAs, payment terms and payroll dates') and explains the two modes with an inline example. It does not explicitly name the sibling alternatives (date_add, date_diff) or exclude cases where a plain calendar-day diff is the right choice, so it stops short of full when/when-not routing.

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