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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), and the description adds substantial context on top: country-specific weekend rules (Friday-Saturday where applicable), national holidays, the fact that every skipped day is named, the deliberate exclusion of province-only holidays and how to apply them, plus pricing and auth mechanics. That goes well beyond what the annotations convey.

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?

Purpose and the two modes are front-loaded, and the province-holiday caveat is well placed. The action is somewhat diluted by the rhetorical 'Net 30 — but which 30, in which country?' opener and the trailing pricing/marketing paragraph, but every sentence still carries information.

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?

An output schema exists, so return formatting need not be described, and the annotations carry the safety profile. The description still supplies coverage scope, mode semantics, and the regional-holiday edge case, leaving nothing an agent needs in order to call it correctly.

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 every parameter (from, to, add, country) is already documented in the schema. The description reinforces the two-mode framing ('add' vs 'to') and the required country input, but adds no syntax, format, or default detail beyond what the schema states. Baseline 3 is appropriate.

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 and resource with unusual precision: 'Add business days to a date, or count them between two dates, for ~110 countries.' The two operating modes are named explicitly, so an agent knows exactly what it does without opening the schema. It never references the closest sibling (holiday_calendar), so sibling differentiation is only implicit, which keeps it out of the top band.

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?

'Built for payment terms, SLAs and delivery dates' gives clear intended-use context, and the auth guidance (x402 vs prepaid x-credit-token, 1 free call/day) tells the agent how to invoke it. There is no explicit when-not-to-use statement or named alternative tool, so it falls short of the 5 band.

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