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

Annotations cover the safety profile (readOnly, idempotent, openWorld), but the description adds critical context they cannot: the upstream source (Nager.Date LongWeekend), the paid x402 USDC-on-Base billing model, the $0.001 per-successful-call price, and the failure path — calling without payment returns a PaymentRequired object. That payment/error disclosure is the materially valuable piece.

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 sentences, both front-loaded: usage/purpose first, behavioral and billing facts second. No filler, and the data source is tucked in without disrupting the flow.

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?

With no output schema, the description still conveys the return content (3+ day windows, bridge-day flag, dates to take off), the source, the cost, and the unpaid-call response. Nothing an agent needs to invoke and interpret this correctly is missing.

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 both params (country as ISO 3166-1 alpha-2, year defaulting to current UTC year) are already fully documented. The description only restates 'for a country and year' and adds no format or defaulting detail beyond the schema, so the baseline 3 applies.

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 ('returns long-weekend windows for a country and year') plus the exact business rule (public holiday creating 3+ consecutive days off) and the payload fields (bridge day needed, dates to take off). This clearly separates it from siblings like holidays, holiday_check, and holidays_next.

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?

Opens with an explicit use case: 'Use for travel or leave planning.' That gives a clear triggering context, but it never states when NOT to use it or names the sibling (holiday_check, holidays) to use for adjacent holiday needs, so the routing guidance stops short of a 5.

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