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

Annotations only cover the safe-read/idempotent profile; the description adds substantial behavior beyond them: it is a paid tool billed via x402 USDC on Base at $0.001 per successful call, and an unpaid call returns a PaymentRequired object rather than failing opaquely. It also discloses the look-ahead behavior (extends into the following year if needed) and that only public calendar data is returned.

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?

A single dense sentence front-loads the decision context, then the outputs, then the payment terms — a sensible priority order with no filler. It is tightly packed but fairly long, and the paid-call mechanics could be one clause shorter, keeping it just below ideal.

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 carries the return-value burden and does so fully: isHoliday boolean, matching holiday record(s), and the next holiday with its look-ahead caveat. Combined with the payment/fallback disclosure, an agent has everything needed to invoke it correctly, including how to handle a non-paying call.

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 (date as YYYY-MM-DD, country as ISO 3166-1 alpha-2) are already fully documented in the schema, establishing the baseline of 3. The description adds only marginal semantics by clarifying that the date anchors both the boolean check and the subsequent next-holiday lookup; no format or edge-case detail is added beyond the schema.

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 exact scope: given a country and date, returns isHoliday true/false, matching holiday record(s), and the next holiday on or after that date. This cleanly separates it from siblings like holidays_next and holidays_long_weekend, which perform different calendar computations.

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?

Front-loads a concrete usage context ('before booking meetings, shipping deadlines or marketplace cut-offs'), which tells the agent the decision scenario this answers. It stops short of naming alternatives (e.g. holidays_next, holidays_countries) or exclusion conditions, so it is clear on when to use but silent on when not to.

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