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

Annotations cover readOnly/openWorld/idempotent, and the description adds substantial context beyond them: the upstream source (Nager.Date LongWeekend), the paid model (x402 USDC on Base, $0.001 per successful call), and crucially the failure protocol — call without payment and you get a PaymentRequired object. That payment/auth behavior is exactly what annotations cannot express.

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 dense sentences, front-loaded with the use case and the returned payload, followed by the source and payment terms. No filler and nothing redundant with the schema.

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 characterizes the return content (long-weekend windows, bridge-day flag, dates to take off), names the data source, and discloses the payment flow. An agent has everything needed to call it and interpret the result 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 both parameters (year, country with ISO 3166-1 alpha-2 and a current-UTC-year default) are already fully documented in the schema. The description adds no parameter syntax or format detail beyond that, 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?

Specific verb and resource: returns long-weekend windows for a country/year where a public holiday creates 3+ consecutive days off, plus bridge-day requirement and dates to take off. This is clearly differentiated from siblings like holiday_check, holidays, holidays_next, and holidays_countries, so an agent can select it without opening another schema.

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?

"Use for travel or leave planning" gives an explicit usage context, which is more than most siblings likely offer. However, it names no alternative tool and gives no when-not condition (e.g., use holidays_next for the next single holiday vs. this for multi-day windows), leaving sibling routing partly to inference.

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